Multiple monochromatic print cartridge printing method

ABSTRACT

A printing method includes the steps of: receiving a colour image and separating the colour image into a plurality of distinct colour planes; dithering a first distinct colour plane to obtain dot data for the first distinct colour plane; dithering a second distinct colour plane to obtain dot data for the second distinct colour plane; providing the dot data for the first distinct colour plane to a first print head cartridge for printing by a plurality of nozzle rows of the first print head cartridge; and providing the dot data for the second distinct colour plane to a second print head cartridge positioned downstream from the first print head cartridge in a direction of print media propagation, the dot data for the second distinct colour plane for printing by a plurality of nozzle rows of the second print head cartridge.

TECHNICAL FIELD

The present disclosure is directed to a colour ink jet printing systememploying a plurality of pagewidth print head cartridges.

CO-PENDING APPLICATIONS

The following applications have been filed by the Applicantsimultaneously with the present application:

HHP001US HHP002US HHP003US HHP004US HHP005USThe disclosures of these co-pending applications are incorporated hereinby reference. The above applications have been identified by theirfiling docket number, which will be substituted with the correspondingapplication number, once assigned.

BACKGROUND

An ink jet print head cartridge designed to provide full colour printsconventionally has a plurality of nozzle rows, one nozzle row forprinting each of the colours Cyan, Magenta, Yellow, and Black.Conventional print head cartridges having this arrangement are operatedsuch that each nozzle row partially contributes to the printing of eachline on a page. Put differently, each full colour line that is printedon the page receives ink from every nozzle row of the print headcartridge.

For example, in printing a colour image, one or more nozzles of a Cyannozzle row of the print head cartridge prints the Cyan coloured dotsthat are needed for a first line on the page. Subsequently, one or morenozzles of a Magenta nozzle row of the print head cartridge prints theMagenta coloured dots that are needed for this same first line on thepage, followed like wise by one or more nozzles in the Yellow row andthe Black row of the print head. In this manner, the first line of thepage receives ink from each of the C, M, Y and K nozzle rows of the oneprint head cartridge, whereby all necessary colours for that first fullcolour line of the page are reproduced.

In the past, ink jet printing systems employed a scanning type printhead cartridge in which a print head cartridge that is significantlynarrower than a width of the page (often 1 or 2 nozzles wide, but manynozzles tall) is scanned/moved across the width of the page to eject inkto all necessary positions on the page. Such systems have had areputation of being slower than other methods of printing, such as alaser printing system.

To address the speed disadvantage of scanning type ink jet printingsystems, pagewidth ink jet printing systems employing a print headcartridge that is stationary, and which spans an entire width of theprint media onto which an image is being printed, have been developed.The printing speeds of such pagewidth ink jet printing systems arecomparable with those of laser printing systems. However, it would bedesirable if the printing speeds of such pagewidth ink jet print systemscould be still further increased without compromising on print quality.

SUMMARY

According to a first embodiment of the present disclosure, a colour inkprinting system comprises a plurality of print head cartridges, eachextending across a direction of print media propagation and spaced apartalong the direction of print media propagation; a print head chassis forsupporting the plurality of print head cartridges, the print headchassis actuable between a printing position, a transition position, anda maintenance position; and a maintenance chassis for supporting aplurality of maintenance cradles, the maintenance chassis actuablebetween a storage position and an operational position. Each of theplurality of print head cartridges is held stationary with respect to aplaten on which print media is propagated to effect printing on theprint media. Each of the plurality of print head cartridges is amonochrome print head cartridge ejecting a fluid different to theremaining plurality of print head cartridges.

In one aspect of the first embodiment, the print head chassis issupported on a platen in the printing position.

In another aspect of the first embodiment, the print head chassis in theprinting position is supported from a pair of gantries suspended above aplaten.

In another aspect of the first embodiment, the print head chassis issupported by the maintenance chassis in the maintenance position.

In another aspect of the first embodiment, the printing position of theprint head chassis is lower than the maintenance position of the printhead chassis.

In another aspect of the first embodiment, the maintenance position ofthe print head chassis is lower than the transition position of theprint head chassis.

In another aspect of the first embodiment, when in the storage positionthe maintenance chassis is retracted from out of a footprint of theprint head chassis.

In another aspect of the first embodiment, when in the operationalposition, the maintenance chassis is positioned under a footprint of theprint head chassis.

In another aspect of the first embodiment, the print head chassisincludes pin bushes at each corner thereof.

In another aspect of the first embodiment, the maintenance chassisincludes positioning pins protruding from each corner thereof, eachpositioning pin adapted to be received in a pin bush of the print headchassis.

In another aspect of the first embodiment, one of the pin bushes of theprint head chassis defines a circular-conical depression for receivingtherein a positioning pin of the maintenance chassis.

In another aspect of the first embodiment, the circular-conicaldepression allows no degree of freedom for movement of the positioningpin within the pin bush in a horizontal plane.

In another aspect of the first embodiment, one of the pin bushes of theprint head chassis defines a oval-conical depression for receivingtherein a positioning pin of the maintenance chassis.

In another aspect of the first embodiment, the oval-conical depressionallows one degree of freedom for movement of the positioning pin withinthe pin bush in a horizontal plane.

In another aspect of the first embodiment, the printing system furthercomprises the platen on which the print media is supported andpropagated.

In another aspect of the first embodiment, the platen comprisespositioning pins protruding respectively from corners thereof, eachpositioning adapted to be received in a pin bush of the print headchassis.

In another aspect of the first embodiment, each positioning pin of theplaten is mechanically engaged with a cam, and the cam is mechanicallyengaged with an adjusting knob, whereby a height of protrusion of thepositioning pins from the plate is adjustable.

In another aspect of the first embodiment, each positioning pin issupported on a spring and biased by the spring to protrude from asurface of the platen, and the platen includes a clamping arrangementarranged around each positioning pin to clamp each positioning pin at adesired protruding height from the surface of the platen.

In another aspect of the first embodiment, the print head chassiscomprises a plurality of supporting arms extending upwards from eachcorner of the print head chassis.

In another aspect of the first embodiment, each supporting arm includesa positioning pin extending downwards towards the print head chassis.

In another aspect of the first embodiment, each supporting arm includesa pin height adjuster for adjusting an extension of each positioning pintowards the print head chassis.

In another aspect of the first embodiment, the printing system furthercomprises a mounting frame attached to a main body of the printingsystem, the mounting frame including a plurality of pin bushes, andwherein the mounting frame is adapted to couple with a gantry suspendedabove the platen.

In another aspect of the first embodiment, the plurality of positioningpins of the supporting arms are adapted to be respectively received inthe plurality of pin bushes of the mounting frame.

In another aspect of the first embodiment, one of the pin bushes of themounting frame defines a circular-conical depression for receivingtherein a positioning pin of the support arms.

In another aspect of the first embodiment, the circular-conicaldepression allows no degree of freedom for movement of the positioningpin within the pin bush in a horizontal plane.

In another aspect of the first embodiment, one of the pin bushes of themounting frame defines a oval-conical depression for receiving therein apositioning pin of the support arms.

In another aspect of the first embodiment, the oval-conical depressionallows one degree of freedom for movement of the positioning pin withinthe pin bush in a horizontal plane.

In another aspect of the first embodiment, the printing system furthercomprises a scissor guide for attaching the print head chassis to a mainbody of the printing system; and a lift mechanism mechanically engagedwith the scissor guide, wherein the scissor guide and lift mechanismeffect linear movement of the print head chassis between the printingposition, maintenance position, and transition position.

In another aspect of the first embodiment, each print head cartridgeincludes a modular printhead made up of a plurality of print head tilesarranged end to end.

In another aspect of the first embodiment, each print head tile definesplural rows of ink ejection nozzles, whereby the print head is made upof a plurality of the print head tiles defines plural rows of inkejection nozzles.

In another aspect of the first embodiment, the plural rows of inkejection nozzles of each print head cartridge all eject ink of the samecolour.

In another aspect of the first embodiment, the plural rows of inkejection nozzles of one print head cartridges eject ink of a firstcolour that is different to a colour of ink ejected by the plural rowsof ink ejection nozzles of another print head cartridge.

In another aspect of the first embodiment, one or more print headcartridges include a plurality of ventilation slits defined in thevicinity of the print head tiles, each ventilation slit having appliedthereto a suction force for sucking ink aerosol particles away from theprint head tiles.

In another aspect of the first embodiment, the one or more print headcartridges each include a ventilation outlet adapted to engage with anaerosol transport means for transporting ink aerosol particles away fromthe print head cartridges.

In another aspect of the first embodiment, the aerosol transport meansis connected to an ink aerosol tank, the ink aerosol tank includingtherein an aerosol filter.

In another aspect of the first embodiment, the printing system furthercomprises a suction device connected to the ink aerosol tank, thesuction device providing the suction force to the plurality ofventilation slits.

In another aspect of the first embodiment, the aerosol transport meansincludes a plurality of hoses, each hose connecting a ventilation outleteach of the one or more print head cartridges to an input port of theink aerosol tank.

In another aspect of the first embodiment, the aerosol transport meansincludes a common transport rail, and a plurality of connectorsconnecting the ventilation outlets of the one or more print headcartridges to the common transport rail, the common transport rail beingfurther connected at one end thereof to the ink aerosol tank.

In another aspect of the first embodiment, each maintenance cradleincludes a capper and a cleaner.

In another aspect of the first embodiment, the maintenance chassisincludes a sub-frame on which the plurality of maintenance cradles aresupported, and the maintenance chassis further includes a motor attachedto the sub-frame, the motor operable to linearly translate the sub-framewithin the maintenance chassis.

In another aspect of the first embodiment, the sub-frame is linearlytranslated within the maintenance chassis to align one of the capper orthe cleaner with respective print head cartridges.

In another aspect of the first embodiment, the capper is providedadjacent to the cleaner, in the direction of print media propagation,and the sub-frame is linearly translated in the direction of print mediapropagation to align one of the capper or the cleaner with respectiveprint head cartridges.

In another aspect of the first embodiment, the cleaner includes a firstroller of a fluid absorptive material, the first roller for wiping aprint head of a respective print head cartridge.

In another aspect of the first embodiment, the cleaner includes a secondroller of a hard material, the second roller for pressing against thefirst roller to squeeze out ink absorbed into the first roller.

In another aspect of the first embodiment, the cleaner includes a wiperblade for scraping the second roller of ink squeezed from the firstroller.

In another aspect of the first embodiment, each maintenance cradleincludes a sump into which the cleaner and capper drain.

In another aspect of the first embodiment, the sump has a sloping floor.

In another aspect of the first embodiment, the sump includes a drainhole at a lower end of the sloping floor.

In another aspect of the first embodiment, the maintenance chassisdefines an ink collection channel along one side thereof, the inkcollection channel for receiving ink from each of the drain holes of theplurality of maintenance cradles.

In another aspect of the first embodiment, the printing system furthercomprises a waste ink collector into which the ink collection channel ofthe maintenance chassis drains, via a channel outlet provided at an endof the ink collection channel.

In another aspect of the first embodiment, the waste ink collector is aflat tray.

In another aspect of the first embodiment, the flat tray has a footprintcovering at least the locus of movement of the channel outlet as themaintenance chassis is actuated between the storage position and theoperational position.

In another aspect of the first embodiment, the flat tray has athickness, and is positioned, such that a bottom of the flat tray is notlower than a print head of the print head cartridges when in theprinting position.

According to a second embodiment of the disclosed invention, a printingmethod, comprises the steps of: receiving a colour image and separatingthe colour image into a plurality of distinct colour planes; dithering afirst distinct colour plane to obtain dot data for the first distinctcolour plane; dithering a second distinct colour plane to obtain dotdata for the second distinct colour plane; providing the dot data forthe first distinct colour plane to a first print head cartridge forprinting by a plurality of nozzle rows of the first print headcartridge; and providing the dot data for the second distinct colourplane to a second print head cartridge positioned downstream from thefirst print head cartridge in a direction of print media propagation,the dot data for the second distinct colour plane for printing by aplurality of nozzle rows of the second print head cartridge.

In another aspect of the second embodiment, the method further comprisesa step of adding a delay to the dot data for the second distinct colourplane, the delay compensating for the spatial separation of the secondprint head cartridge from the first print head cartridge.

In another aspect of the second embodiment, the method further comprisesa step of vertically shifting the dot data for the first distinct colourplane by one or more nozzle rows in a direction of print mediapropagation, to advance and delay printing of the first distinct colourplane by the first print head cartridge by one or more nozzle rows,wherein a physical misalignment of the first print head cartridge in adirection of print media propagation with respect to the second printhead cartridge is compensated.

In another aspect of the second embodiment, the method further comprisesa step of vertically shifting the dot data for the second distinctcolour plane by one or more nozzle rows in a direction of print mediapropagation, to advance and delay printing of the second distinct colourplane by the second print head cartridge by one or more nozzle rows,wherein a physical misalignment of the second print head cartridge in adirection of print media propagation with respect to the first printhead cartridge is compensated.

In another aspect of the second embodiment, the method further comprisesa step of reordering the dot data for the first distinct colour plane toaccount for the physical separation of a first of the plurality ofnozzle rows of the first print head cartridge from a last of theplurality of nozzle rows of the first print head cartridge.

In another aspect of the second embodiment, the method further comprisesa step of reordering the dot data for the second distinct colour planeto account for the physical separation of a first of the plurality ofnozzle rows of the second print head cartridge from a last of theplurality of nozzle rows of the second print head cartridge.

In another aspect of the second embodiment, the method further comprisesfurther comprising a step of horizontally shifting the dot data for thefirst distinct colour plane by one or more dot pitches in a directionnormal to a propagation of print media, wherein a wobbling of the printmedia in a direction normal to the propagation of print media iscompensated.

In another aspect of the second embodiment, the method further comprisesa step of horizontally shifting the dot data for the second distinctcolour plane by one or more dot pitches in a direction normal to apropagation of print media, wherein a wobbling of the print media in adirection normal to the propagation of print media is compensated.

According to a third embodiment of the disclosed invention, a printingmethod comprises the steps of: receiving a colour image and separatingthe colour image into a plurality of distinct colour planes; separatingeach distinct colour plane into a plurality of fake colour planes;arranging the plurality of fake colour planes corresponding to onedistinct colour plane into a fake colour image logically comprised of acomposite of fake colour planes; and presenting the fake colour image toa multi-coloured print engine of a print head cartridge having aplurality of nozzle rows for printing.

In another aspect of the third embodiment, the method further comprisesa step of separating the fake colour image in the multi-coloured printengine to obtain the fake colour planes, generating print data for eachfake colour plane, and sending the print data for a first fake colourplane to a first nozzle row of the print head cartridge and sending theprint data for a second fake colour plane to a second nozzle row of theprint head cartridge different to the first nozzle row.

In another aspect of the third embodiment, the method further comprisesa step of increasing a speed of print media propagation past the printhead cartridge to prevents dots printed by the second nozzle row fromlanding on dots printed by the first nozzle row.

According to a fourth embodiment of the disclosed invention, a methodfor aligning a plurality of print head cartridges arranged in a printingsystem along a print media propagation path, where each print headcartridge has a plurality of print head tiles arranged end-to-end tospan a width of the print media propagation path, comprises the stepsof: selecting a first print head cartridge as a reference print headcartridge; printing a first plurality of Vernier patterns using thereference print head cartridge, each of the first plurality of Vernierpatterns corresponding to a print head tile of the reference print headcartridge; printing a second plurality of Vernier patterns over thefirst plurality of Vernier patterns using a second print head cartridge;and determining, from an interference pattern generated from theprinting of the second plurality of Vernier patterns over the firstplurality of Vernier patterns, a distance of separation along the printmedia propagation path of each of the plurality of print head tiles ofthe second print head cartridge from corresponding print head tiles ofthe reference print head cartridge.

DESCRIPTION OF DRAWINGS

FIG. 1A is a front perspective view of a printing system according tothe disclosed invention, in the transition position.

FIG. 1B is a front perspective view of a printing system according tothe disclosed invention, in a printing position.

FIG. 1C is a front perspective view of a printing system according tothe disclosed invention, in a maintenance position.

FIG. 1D is a top plan view of a printing system according to thedisclosed invention.

FIG. 2A is a top perspective view of a print head chassis.

FIG. 2B is a bottom perspective view of a print head chassis.

FIG. 2C is a top plan view of a print head chassis.

FIG. 3A is a top perspective view of a maintenance chassis.

FIG. 3B is a bottom perspective view of a maintenance chassis.

FIG. 4A is a top perspective view of a maintenance chassis sub-frame.

FIG. 4B is a bottom perspective view of a maintenance chassis sub-frame.

FIG. 4C is a top perspective view of a maintenance chassis main frame.

FIG. 5A is a top perspective view of a maintenance cradle.

FIG. 5B is a bottom perspective view of a maintenance cradle.

FIG. 6 is a rear perspective view of a printing system according to thedisclosed invention.

FIG. 7 is a plan view of an ink blade.

FIG. 8A is a top perspective view of a platen assembly.

FIG. 8B is a bottom perspective view of a platen assembly.

FIG. 9 is a compilation view of a location bush.

FIG. 10 is a compilation view of a slotted location bush.

FIG. 11 is a compilation view of a flat pin bush.

FIG. 12 is a plan view of a print head cartridge, schematicallyillustrating an arrangement of nozzle and nozzle rows on a print headtile.

FIG. 13 illustrates a Vernier calibration map of the disclosedinvention.

FIG. 14 illustrates a Vernier pattern.

FIG. 15 is a schematic diagram of a reference line sensor.

FIGS. 16A-16D are a flow chart illustrating a process for preparing animage for printing by the printing system of the disclosed invention.

FIGS. 17A and 17B are a flow chart illustrating a process for preparingdot data for a print head cartridge of the disclosed invention.

FIGS. 18A and 18B are a flow chart illustrating a process for generatingfake colour images for printing by the printing system whenmulti-coloured print head cartridges instead of monochrome print headcartridges are employed.

FIG. 19 is a flow chart illustrating a process for printing a fakecolour image.

FIG. 20 illustrates a print head chassis having an aerosol extractionsystem according to a second embodiment of the disclosed invention.

FIGS. 21 and 21A illustrate a printing system according to a thirdembodiment of the disclosed invention.

FIGS. 22 to 24 illustrate a platen according to a fourth embodiment ofthe disclosed invention.

FIGS. 25 and 26 illustrate a waste ink drainage system according to afifth embodiment of the disclosed invention

DETAILED DESCRIPTION Overview

One solution for increasing the printing speed of a page with colour inkjet printing system is to increase the number of pagewidth colour printhead cartridges present in the printer. A mere provision of multiplepagewidth colour print head cartridges does not, however, necessarilyobtain desired, expected, or acceptable results. The inventors of thepresent invention have found that simply employing multiple pagewidthcolour print head cartridges to print what a single pagewidth colourprint head cartridge would print results in a printed image ofsubstantially compromised quality. The issues involved in utilizingmultiple pagewidth colour print head cartridges are described below.

A pagewidth colour print head cartridge may be thought of as comprisinga number of logical rows of nozzles, each for ejecting dots of aspecific colour, for example Cyan, Magenta, Yellow, Black, or a spotcolour (e.g. Khaki). For the purposes of this description, it is assumedthat a pagewidth colour print head cartridge has 5 logical rows, one foreach of the above mentioned colours. At a given instant during theprinting of a full colour image on a sheet of print media, an operationof the pagewidth colour print head cartridge can be thought of as afirst logical row (e.g. Magenta) of the print head cartridge printing afirst line of Magenta dots, a second logical row (e.g. Cyan) printing asecond line of Cyan dots in close vicinity to the first line, a thirdlogical row (e.g. Yellow) printing a third line of Yellow dots in closevicinity to the first and second lines, and so forth.

At a subsequent instant, the operation of the pagewidth colour printhead cartridge can be thought of as the first logical row (e.g. Magenta)printing a new line of dots overlapping the second line of dots (e.g.Cyan) printed by the second logical row in the previous instant. Thesecond logical row (e.g. Cyan) printing a new line of dots overlappingthe third line of dots (e.g. Yellow) printed by the third logical row inthe previous instant, and so forth. Ultimately, by the time the printmedia is propagated a distance equivalent to the footprint of the fivelogical rows of nozzles, there will be printed on the print media five(or more) lines of full colour dots and four (or more) lines of partialcolour dots.

In a system that employs, for example, 5 pagewidth colour print headcartridges positioned across the print media and one after the otheralong a direction of print media propagation, a speed at which the printmedia is propagated is increased such that the five logical rows of asingle printhead cartridge do not ejects dots on top of each other.Instead, a first pagewidth colour print head cartridge prints five linesof different colours (e.g. Black, Cyan, Magenta, Yellow, and Khaki), anda latter (downstream) pagewidth colour printhead cartridge does the samebut is configured to eject its dots on top of the five lines ofdifferent colours ejected by the first pagewidth colour print head. Inthis manner, a full colour image is printed at a speed 5 times fasterthan if only one pagewidth colour print head cartridge is used.

However, the inventors of the present invention found that a systememploying 5 pagewidth colour print head cartridges operated in the abovedescribed manner causes printing defects that are extremely difficult tocompensate for. These defects are described as follows.

In a system utilizing multiple pagewidth colour print head cartridgespositioned across the print media and one after the other along adirection of print media propagation, it is inevitable that a certainamount of misalignment between the print head cartridges will occur. Oneof such misalignments is a misalignment in the distance separatingcolour print head cartridges (i.e. a pitch/spacing interval).

If the system is set up such that each colour print head cartridgeshould be exactly 8 cm from neighbouring print head cartridges,significant printing defects are observed when this ideal is not exactlymet. Since it is expected in such a system for a first print headcartridge to print a first group of 5 lines, each line of a differentcolour, and a second print head cartridge to later print another groupof 5 lines, again each line being of a different colour, over the firstgroup of 5 lines, it can be appreciated that a misalignment of just onerow in the distance separating the first and second print headcartridges results in all 5 lines being printed with the wrong mix ofcolours.

For example, if the logical rows of the second print head cartridge wereone row too far from the first print head cartridge, the first line ofdots printed by the second print head cartridge would overlap with thesecond lines of dots printed by the first print head cartridge, thesecond line of dots printed by the second print head cartridge wouldoverlap with the third line of dots printed by the first print headcartridge (instead of the second line), the third line of dots printedby the second print head cartridge would overlap with the fourth line ofdots printed by the first print head cartridge (instead of the thirdline), and so on up to the last line of dots printed by the second printhead cartridge overlapping with nothing (instead of the last lineprinted by the first print head cartridge).

This problem is exponentially exacerbated the greater the number ofprint head cartridges being used. In a system utilizing 5 pagewidthprint head colour cartridges, this problem becomes extremely complicatedand difficult to compensate for. One print head cartridge may be tooclose to a neighbour on one side, and also too close to a neighbour onanother side, the neighbouring print head cartridge may likewise bemisaligned from its neighbours, and so forth.

Moreover, pagewidth print head cartridges are generally made up of anumber of individual print head tiles arranged end-to-end to span thewidth of the pagewidth print head cartridge. It is again inevitable thatone or more print head tiles may not exactly line up with the rest ofthe print head tiles making up the pagewidth print head cartridge. Oneor more print head tiles may for example be relatively higher or lowerthan the rest of the print head tiles. Accordingly, one print head tilemay be too near a print head tile of a neighbouring print headcartridge, while another print head tile may be too far from theneighbouring print head cartridge. It can be appreciated that thepossible combinations for the plurality of print head tiles of one printhead cartridge to be too near/far from those of neighbouring print headcartridges, which could themselves be too near/far from otherneighbouring print head cartridges, is large.

Other misalignments stem from the fact that pagewidth print headcartridges are rarely perfectly straight. Variations in the fabricationof the pagewidth print head cartridges commonly result in print headcartridges being slightly bowed in a random direction. Hence, not onlymay a line of dots printed by a print head cartridge be slightly bowedin a random direction, a distance separating the logical rows of oneprint head cartridge from those of neighbouring print head cartridgesmay vary depending on which part of the row a nozzle is in. The nozzlesin the middle of a logical row may be at the ideal separation from thelogical row of a neighbouring print head cartridge, but the nozzles atthe ends of the logical row may be too near or too far. How near or howfar the logical rows of neighbouring print head cartridges are to eachother depends on the amount of bowing of each print head cartridge, andthe direction/orientation of the bowing of the print head cartridge andits neighbours.

Still further misalignments between print head cartridges occur due tothermal expansion and contraction in the print head cartridgesthemselves, and also in the structure supporting the print headcartridges. Thermal expansion, as well as causing other types ofmisalignment, also causes misalignment in the distance separating alogical row of a print head cartridge from a logical row of aneighbouring print head cartridge.

Since each pagewidth colour print head cartridge prints one line of eachcolour, each pagewidth colour print head cartridge can be thought of aspartially contributing to the printing of each monochrome image thatmakes up the full colour image (a full colour image is a superpositionof a plurality of monochrome images). Each monochrome image is thereforeprinted in portions, and can be considered a patchwork of portionspieced together. Each portion exhibits the misalignments specific to theprint head cartridge that printed that portion. Accordingly, it can beappreciated that each monochrome image is itself an image exhibitinggreat variation in dot placement, including variation caused by thedifferent degrees and directions of bowing of each print head cartridge,the distance separating each print head cartridge, and also a lateral(side-to-side) misalignment of the print head cartridges.

With each monochrome image exhibiting great variation in dot placement,and with the variation being different amongst monochrome images, andindeed, different even amongst portions of the same monochrome image, afull colour image resultant from a compositing of the monochrome imagesover each other exhibits significant visual defects. After taking intoaccount the chance of misalignment in the distance separating logicalrows of different print head cartridges, the chance of misalignment ofindividual print head tiles making up a print head cartridge, the bowingof print head cartridges, the effect of thermal expansion on the printhead cartridges, and the fact that each monochrome image is misaligneddifferently depending on which portion of the monochrome image is beingconsidered, the chances of perfectly overlapping as many as 5 or moredots of different colours on top of each other is slim.

The inventors have found that a colour image printed using a systememploying 5 pagewidth colour print head cartridges exhibits an obviousinterference pattern.

For the above reasons, the present invention utilizes multiple pagewidthmonochrome print head cartridges. By using multiple pagewidth monochromeprint head cartridges instead of multiple pagewidth colour print headcartridges, every line of each monochrome image that makes up a fullcolour image is printed by one specific pagewidth print head cartridge.Accordingly, any visible errors (e.g. bowing, misalignment between printhead tiles, etc.) caused by imperfect alignment of the components makingup the print head cartridge, such as print head tiles, are lessobjectionable because they are consistent throughout each monochromeimage. In essence, 5 full and visually acceptable monochrome images areprinted. It is then necessary only to align the monochrome image (i.e.22-image, M-image, Y-image, K-image, Spot-image) printed by eachpagewidth monochrome print head cartridge such that each monochromeimage substantially overlaps the others, to produce the full colourimage. This is compared to a system utilizing 5 pagewidth colour printhead cartridge which each partially contribute to the printing of all 5monochrome images, resulting in none of the 5 monochrome images beingvisually acceptable due to the significant variations and misalignmentsdescribed above, and then trying to compensate and correct each of the 5monochrome images as well as align them on top of each other.

It is accepted that each monochrome image may not perfectly align withevery other monochrome image, resulting in, for example, at a certainpoint on the page, a “cyan” dot not landing exactly on top of a“magenta” dot, causing a slight localised colour error. However, thisloss of print quality resulting from localised imperfect colourplacement is perceptually far less visible than the loss of printquality resulting from the printing of self-inconsistent monochromeimages caused by printing each monochrome image using 5 different printheads.

The employment of multiple print head cartridges introduces structuraland mechanical complexities such as how such multiple print headcartridges should be supported, how to effect maintenance and cleaningfor the multiple print head cartridges, how to maintain consistenttolerances and spacing between the print head cartridges and the printmedia, how to correct for misalignment between the multiple print headcartridges, and the like. Solutions to these issues used in a singleprint head cartridge (SPHC) printing system do not necessarily lendthemselves as solutions for a multiple print head cartridge (MPHC)printing system. Moreover, some of these issues simply do not exist inSPHC printing systems.

For example, in a SPHC printing system, a maintenance and cleaningmechanism may be attached in close proximity to a print head of theprint head cartridge, such that the maintenance and cleaning mechanismand/or print head can be easily actuated into position when necessary toclean/maintain the print head. In a MPHC system, however, such asolution would result in a substantial increase in the mechanicaldensity of components in and around the print head cartridges, which inturns results in a need for higher tolerances, bettercooling/ventilation, and/or a larger overall footprint of the system.

Moreover, any movement of print heads in a MPHC printing system has totake into consideration pre- and post-movement alignment of the printhead cartridges with respect to other print head cartridges, and furtherwith respect to a platen of the printing system. If one print headcartridge is moved for the reason of, for example, cleaning andmaintenance, it must be considered if the print head cartridge can bemoved back to exactly the same position it was in before movement. Inconsideration of the fact that cleaning and maintenance is a relativelyregular event, and that this event is performed for each print headcartridge, it becomes easy to appreciate the exponential increase incomplexity as compared to an SPHC system. Misalignments of one printhead cartridge with respect to other print head cartridges introducesprinting defects which clearly do not occur in a SPHC printing system.

Mechanical Structure First Embodiment

FIGS. 1A to 1D illustrate a printing system 1-1000 according to a firstembodiment of the present invention. The printing system 1-1000 has aprint head chassis 1-10 for holding multiple print head cartridges 1-20a, 1-20 b, 1-20 c, 1-20 d, 1-20 e (see FIG. 1D) and corresponding printhead controller modules 1-25 a, 1-25 b, 1-25 c, 1-25 d, 1-25 e. Forpurposes of clarity, the figures illustrate only one print headcartridge 1-20 a. However, reference numerals 1-20 b, 1-20 c, 1-20 d,and 1-20 e are used to indicate where the remaining print headcartridges are located.

In the illustrated embodiment, five print head cartridges 1-20 a-e areprovided in the printing system 1-1000. Each print head cartridge 1-20a-e spans a width of the print media 1-200. The five print headcartridges 1-20 a-e are positioned one after another along a directionof print media propagation, that is, in the X-direction as indicated bythe axes in FIG. 1A.

Each print head cartridge 1-20 a-e is connected to respective monochromeink supply modules 1-90 a,1-90 b,1-90 c,1-90 d, 1-90 e. Each print headcartridge 1-20 a-e prints ink of a single colour/property only. This isin contrast to a SPHC printing system, and a scanning-type printingsystem, in which one print head cartridge ejects inks of multiplecolours. In one exemplary embodiment, each print head cartridge 1-20 a-eprints one of Cyan, Magenta, Yellow, Black, and a spot colour (e.g.Khaki), however, any combination of colours may be printed by the printhead cartridges 1-20 a-e.

It should be understood that the disclosed invention is not limited toonly five print head cartridges, and may comprise any number from two ormore print head cartridges. Further, for simplicity and conciseness ofdescription, while the fluids ejected by the print head cartridges 1-20a-e are referred to herein as “inks”, it is to be understood that theterms “ink” and “inks” refer to any fluid that may be ejected by theprint head cartridges 1-20 a-e including a fixative, a glue or otherbonding substance, fluidic semiconductor material, and the like.Similarly, while the inks are referred to as having a “colour”, it is tobe understood that the term “colour” is used to refer broadly to theproperties of the fluids ejected by the print head cartridges 1-20 a-e,rather than strictly to a colour in the human visible spectrum.

Accordingly, and as already alluded to above, a fixative may be referredto as an “ink” in the present disclosure, and may also be referred to ashaving a “colour” in the sense that the fixative has a property thatdistinguishes it from the other inks. It follows that a print headcartridge that receives monochromatic ink refers to a print headcartridge that receives ink/fluid of only one colour/property”, such ascyan ink, magenta ink, yellow ink, black ink, infrared ink, a fixative,a glue, a semiconductor material in fluid state, and so forth.

The print head cartridges 1-20 a-e are stand-alone cartridges that areindividually removable from the print head chassis 1-10. A print headcartridge 1-20 is illustrated in greater detail in FIG. 12. The printhead cartridge 1-20 comprises a plurality of print head tiles 12-10arranged end-to-end along a length (i.e. Z-axis of FIG. 1A) of the printhead cartridge. FIG. 12 illustrates 11 print head tiles 12-10 arrangedend-to-end to form the page width print head cartridge 1-20 however itshould be understood that more or less than 11 print head tiles may beemployed, as necessary to span a width of the print media 1-200.

Each print head tile 12-10 has a plurality of logical rows 12-20. InFIG. 12, each print head tile 12-10 is illustrated with 5 logical rows12-20, however a lesser or greater number of logical rows may beprovided. Each logical row 12-20 is divided into a pair of sub-rows12-30, 12-40, which sub-rows are offset with respect to each other alonga length (i.e. Z-axis of FIG. 1A) of the print head cartridge 1-20. Thefirst sub-row 12-30 of each row 12-20 prints odd numbered dots for aline on a page, whilst the second sub-row 12-40 prints even numbereddots for the same line on the page, or vice versa. Whilst FIG. 12 showsone logical row 12-20 as being comprised of two adjacent sub-rows 12-30,12-40, a logical row may in fact be comprised of any even dot printingsub-row 12-30 and any odd dot printing sub-row 12-40, not necessarilyadjacent to each other

The print head cartridges 1-20 a-e are spaced from each other along awidth of the printing system 1-1000 (i.e. X-axis of FIG. 1A), that is,along a direction of print media propagation. Compared to the size ofthe dots printed by the print head cartridges 1-20 a-e, the spacingbetween the print head cartridges 1-20 a-e is very large, and measuredin standard units of length (i.e. mm, cm, inches, etc.). In oneembodiment, the print head cartridges 1-20 a-e are spaced at 8 cmintervals from each other.

The print head chassis 1-10 is attached via scissor guide 1-40 to theprinter main frame 1-50. The scissor guide 1-40 and a lift mechanism1-60, together with a pair of wires (not shown) interconnecting thescissor guide 1-40 and the lift mechanism 1-60 actuate the print headchassis 1-10 between a printing position, a transition position, and amaintenance position.

FIG. 1A illustrates the printing system 1-1000 while in the transitionposition. In the transition position, the print head chassis 1-10 isheld at a height, relative to the platen 1-70, that allows for themaintenance chassis 1-80 to be manoeuvred under the print head chassis1-10 without being interfered with by the print head chassis 1-10. Inparticular, the transition position allows the maintenance chassis 1-80to retract to and from a storage position under the ink supply modules1-90 a-e, and an operational position under the print head chassis 1-10.

FIG. 1B illustrates the printing system 1-1000 while in the printingposition. In FIG. 1B, the printer main frame 1-50 is illustrate with oneside thereof removed, to more clearly show the components housedtherein. In the printing position, the print head chassis 1-10 ispositioned in close proximity to the platen 1-70 to enable printing bythe print head cartridges 1-20 a-e onto the print media 1-200propagating across the platen 1-70.

FIG. 1C illustrates the printing system 1-1000 while in the maintenanceposition. In the maintenance position, the print head chassis 1-10 ispositioned some distance above the platen 1-70, and the maintenancechassis 1-80 is positioned in an operational position interposed betweenthe platen 1-70 and the print head chassis 1-10. In the maintenanceposition, the print head 1-10 is supported by the maintenance chassis1-80.

In one aspect of the present invention, the platen 1-70 is part of theprinting system 1-1000. In other aspects, however, the printing system1-1000 does not include the platen 1-70, and the platen 1-70 is insteadconfigured and designed by a third party and/or an end-user. In thefirst embodiment, however, the platen 1-70 is provided with positioningpins 1-100 a, 1-100 b, 1-100 c, 1-100 d (see also FIG. 8A) which couplewith pin bushes 2-100 a, 2-100 b, 2-100 c, 2-100 d on an underside ofthe print head chassis 1-10 (see also FIG. 2B). The positioning pins1-100 a, 1-100 b, 1-100 c, 1-100 d, as illustrated in FIG. 8A,preferably have a rounded, dome head which facilitates more accuratecoupling and positioning with the pin bushes 2-100 a, 2-100 b, 2-100 c,2-100 d. The platen 1-70 includes a source of the print media 1-200, anda feed mechanism 1-210 for feeding the print media 1-200 across aprinting surface 1-220 of the platen 1-70. An encoder wheel 1-230 isincluded with the platen 1-70 for measuring a speed of the print media1-200 as it is propagated across the platen 1-70. The speed measured bythe encoder wheel 1-230 is used to time and synchronize an operation ofthe print head cartridges 1-20 a-e.

FIGS. 2A and 2B illustrate in greater detail the print head chassis 1-10and the print head cartridges 1-20 a-e. In FIGS. 2A and 2B, only oneprinthead cartridge 1-20 a is again shown for purposes of clarity.

As shown in FIG. 2A, the print head controller modules 1-25 a-e, and theprint head cartridges 1-20 a-e are equally spaced apart in the printhead chassis 1-10. Each print head cartridge 1-20 a-e is removablyengaged with the print head chassis 1-10 via corresponding locking tabs2-40.

The print head controller modules 1-25 a-e are engaged with the printhead chassis 1-10 so as to be pivotable towards and away from arespective print head cartridge 1-20 a-e through actuation of respectivelocking mechanisms 2-10 a, 2-10 b, 2-10 c, 2-10 d, 2-10 e. Each printhead controller module 1-25 a-e electrically engages with a respectiveprint head cartridge 1-20 a-e by pivoting towards the respective printhead cartridge 1-20 a-e such that a row of electrical connectors 1-500(see detailed cutout) on each print head controller module 1-25 a-epushes against the respective print head cartridge 1-20 a-e. Each printhead controller module 1-25 a-e is locked in electrical engagement withrespective print head cartridges 1-20 a-e by locking mechanisms 2-10 a,2-10 b, 2-10 c, 2-10 d, and 2-10 e.

In an aspect of the print head chassis 1-10, an ink aerosol filter 2-20is provided at one end of the chassis to collect and filter aerosolparticles of ink arising from each print head cartridge 1-20 a-e. Theink aerosol filter 2-20 is connected via hoses (not shown) toventilation outlets 2-30 a, 2-30 b, 2-30 c, 2-30 d, 2-30 e, 2-30 f (seealso FIG. 2C) respectively connected to suction slits 2-35 a, 2-35 b,2-35 c, 2-35 d, 2-35 e, 2-35 f (see FIG. 2B) provided in the vicinity ofeach print head cartridge 1-20 a-e.

The aerosol filter 2-20 includes inlet ports 2-25 to which the hosesfrom respective ventilation outlets 2-30 a, 2-30 b, 2-30 c, 2-30 d, 2-30e, 2-30 f connect, and an outlet port 2-28 which preferably connects toa further filter such as a HEPA filter, and then to a suction device.

Pin bushes 2-100 a, 2-100 b, 2-100 c, 2-100 d are provided on each ofthe four bottom corners of the print head chassis 1-10. Pin bushes 2-100a, 2-100 b, 2-100 c, 2-100 d support the print head chassis 1-10 (asdescribed in greater detail below), and further provide an aligningfeature for ensuring proper alignment of the print head chassis 1-10with the maintenance chassis 1-80 and, in the first embodiment, theplaten 1-70.

FIGS. 3A and 3B illustrate the maintenance chassis 1-80 in greaterdetail. The maintenance chassis 1-80 includes print head maintenancecradles 3-20 a, 3-20 b, 3-20 c, 3-20 d, 3-20 e. Each print headmaintenance cradle includes a capper 3-25 and a cleaner 3-27. The capper3-25 provides the function of sealing a print head of a print headcartridge 1-20 a-e when the print head cartridge is not in used, and toalso serve as a spittoon in which ink from the print head cartridge isejected for priming and cleaning purposes. Positioning pins 3-50 a, 3-50b, 3-50 c, 3-50 d are provided at each corner of the maintenance chassis1-80. Positioning pins 3-50 a, 3-50 b, 3-50 c, 3-50 d are similar to thepositioning pins 1-100 a, 1-100 b, 1-100 c, 1-100 d on the platen 1-70in that they are for coupling with pin bushes 2-100 a, 2-100 b, 2-100 c,2-100 d provided on an underside of the print head chassis 1-10. Thepositioning pins 3-50 a, 3-50 b, 3-50 c, 3-50 d preferably have arounded, dome head.

The maintenance chassis 1-80 includes a maintenance chassis sub-frame3-10 (see also FIG. 4A) on which the print head maintenance cradles 3-20a-e are supported, and a maintenance chassis main frame 4-50 withinwhich the maintenance chassis sub-frame 3-10 resides. The maintenancechassis sub-frame 3-10 is movable within the maintenance chassis mainframe 4-50. A sub-frame movement mechanism 3-40 (see FIG. 3A) isprovided on the maintenance chassis main frame 4-50 and connected to themaintenance chassis sub-frame 3-10 by a connection member 3-30 to effectmovement of the maintenance chassis sub-frame 3-10, and hence the printhead maintenance cradles 3-20 a-e, with respect to the maintenancechassis main frame 4-50. The maintenance chassis sub-frame 3-10 is movedwith respect to the maintenance chassis main frame 4-50 to allow eitherthe capper 3-25 or the cleaner 3-27 to be aligned with the print headcartridges 1-20 a-e.

FIGS. 4A and 4B illustrates the maintenance chassis sub-frame 3-10 ingreater detail. FIG. 4C illustrates the maintenance chassis main frame4-50 in greater detail. The maintenance chassis sub-frame 3-10 has apair of rails 4-10 which engage with rail supports 4-15 of themaintenance chassis main frame 4-50 allowing the maintenance chassissub-frame 3-10 to slide within the maintenance chassis main frame 4-50.Each print head maintenance cradle 3-20 a-e is supported between thepair of rails 4-10, and spaced equally apart with a pitch matching thatof the spacing between the print head cartridges 1-20 a-e, as requiredto either clean or cap the print head cartridges 1-20 a-3.

As best shown in FIG. 5A, the cleaner 3-27 includes a first roller 3-29of a microfiber material and a second roller 3-28 made of stainlesssteel or other suitable hard material. The first roller 3-29 providesthe function of wiping a print head and wicking ink therefrom, whilstthe second roller 3-28 serves the function of pressing against the firstroller 3-29 to cause ink soaked thereinto to be squeezed out. A wiperblade 3-24 is also included in each print head maintenance cradle 3-20a-e to scrape from the second roller 3-28 any ink that is squeezed outfrom the first roller 3-29.

Each print head maintenance cradle 3-20 a-e further includes a rollerdriver 3-30 for driving the first and second rollers 3-28, 3-29, and asump 3-40 for collecting ink received by the cleaner 3-27 and the capper3-25. The sump 3-40 has a sloping floor 3-45 (see FIG. 5B) having alowest point at one end of the maintenance cradle 3-20 a-e. As shown inFIG. 5B, the floor of the sump 3-40 has a drain hole 3-48 from which inkcollected in the sump drains. The drain holes 3-48 of each maintenancecradle 3-20 a-e drain into an ink collection channel 3-60 (see FIG. 4C)provided along one side of the maintenance chassis main frame 4-50. Theink collection channel 3-60 connects with a series of channels providedin the printer main frame 1-50 to empty into a waste ink tank 6-30 (seeFIG. 6).

The maintenance chassis 1-80 is provided with rollers 3-70 (see FIG. 4C)on two opposing sides of the chassis. The rollers 3-70 allow themaintenance chassis 1-80 to extend and retract between a storageposition (as shown in FIG. 1B) and an operational position (as shown inFIGS. 1A and 1C). A motor 3-80 attached to the maintenance chassis mainframe 4-50 engages with a toothed rack 3-90 on the printer main frame1-50 to translate the maintenance chassis 1-80 between the storageposition and the operational position.

FIG. 6 provides a view of the printing system 1-1000 from the rear. Forclarity of illustration, all but one ink blade 1-90 e is removed fromrespective ink blade docking slots. The maintenance chassis 1-80 is alsoshown transitioning to an operational position under the print headchassis 1-10.

The waste ink tank 6-30 is secured to a floor of the main chassis 1-50.As previously described, the waste ink tank 6-30 stores ink received bythe capper 3-25 as a result of a purging or priming operation, and inkreceived by cleaner 3-27 as a result of cleaning the print headcartridges 1-20 a-e.

Each ink blade 1-90 a-e is slidable in a rearward direction (i.e.negative Z-direction of axis on FIG. 1A) to remove the ink blade fromthe main chassis 1-50. In this manner, convenient exchanging of inkblades to change a colour to be printed by a particular print head isfacilitated.

FIG. 7 illustrates one of the ink blades 1-90 a-e in greater detail. Forpurposes of FIG. 7, the ink blade depicted is given reference numeral7-10. The ink blade 7-10 is provided as a blade chassis 7-15 on whichthe components of the ink blade 7-10 are mounted and supported. Theblade chassis 7-15 defines a back plate 7-20 on which an ink inlet 7-30is provided. The ink inlet 7-30 receives ink from an external bulk inksource (not shown) via an inlet hose 7-40 and communicates the ink to aninput 7-60 of a bulk ink pump 7-80. An output 7-70 of the bulk ink pump7-80 connects to a bulk ink input 7-90 of an intermediate reservoir7-50.

An ink filter 7-100 is provided downstream from the intermediatereservoir 7-50 and connects to an ink manifold 7-110. The ink manifold7-110 is connected to a pinch valve 7-120, which in turn communicatesink to the print head. A hose carrier 7-130 is provided to support thehoses (not shown) connecting the pinch valve 7-120 to the print head.Return hoses (not shown) for returning ink from the print head to theintermediate reservoir 7-50 may also be supported on the hose carrier7-130. The return hoses (not shown) from the print head connect to aprinting ink pump 7-140, which in turn connects back to the intermediatereservoir 7-50. The printing ink pump 7-140 is down stream from theprint head and essentially sucks in through the print head, as opposedto pushing ink to the print head. A negative pressure pump 7-150 isfurther provided to maintain a negative pressure in the intermediatereservoir 7-50.

The ink manifold 7-110 defines a plurality of outlets 7-85 which allconnect ultimately to a single print head cartridge 1-20 a, 1-20 b, 1-20c, 1-20 d, or 1-20 e. In this manner, each print head cartridge 1-20 a-eis supplied with ink from a single ink blade 7-10, and hencemonochromatically supplied with ink of a single colour. The colour ofink supplied to a print head cartridge 1-20 a-e is changeable byreplacing the ink blade 7-10 connected thereto, and performing asuitable re-priming process to flush existing ink from the print headcartridge 1-20 a-e and priming the print head cartridge 1-20 a-e withnew ink. Although, preferably, an entire print head cartridge 1-20 a-eis replaced when exchanging ink blades 7-10, whereby the colours printedby the printing system 1-1000 may be rapidly changed to suit differentprint jobs.

FIGS. 8A and 8B show front and rear perspective views, respectively, ofthe platen 1-70. As previously described, the platen 1-70 is part of theprinting system 1-1000 in some aspects. In other aspects, the platen1-70 is provided by a third party or the end user, and configured towork with the printing system 1-70.

The platen 1-70 is a vacuum platen and allows the provision of a suctionforce through the platen surface 1-220 to assist in maintaining a printmedia 1-200 traversing across the surface 1-220 of the platen 1-70 flatagainst the surface 1-220. The surface 1-220 of the platen 1-70 definesdepressions 8-10. Suction holes 8-15 are defined in each depression8-10, which pass through the surface 1-220 of the platen 1-70 to anopposite side. A vacuum box may be attached to an underside of theplaten 1-70, in which one or more suction devices are provided togenerate a suction force downwards through the platen 1-70.

The positioning pins 1-100 a, 1-100 b, 1-100 c, 1-100 d are supported onan adjustment cam system 8-20, which allows for the height of thepositioning pins 1-100 a, 1-100 b, 1-100 c, 1-100 d to be adjusted viaadjustment knob 8-30.

FIGS. 9, 10, and 11 illustrate in detail the pin bushes 2-100 a, 2-100b, 2-100 c, 1-120 d located on an underside of the print head chassis1-10.

Pin bush 2-100 a located at a front-right under-corner of the print headchassis 1-10 when in an operative position is a location bush having ashape and configuration as illustrated in FIG. 9. For convenience ofreference, the location bush illustrated in FIG. 9 is given thereference numeral of 9-100. The location bush 9-100 has a circular head9-10. The circular head 9-10 defines a circular-conical depression 9-20.The circular-conical depression 9-20 is adapted to receive positioningpins 1-100 a and 3-50 a therein. Due to the circular-conicalconfiguration of the depression 9-20 and the rounded head of positioningpins 1-100 a and 3-50 a, the pins 1-100 a and 3-50 a always couple withthe location bush 9-100 in a consistent and exact engagement.

Pin bush 2-100 b located at a front-left under-corner of the print headchassis 1-10, when in an operative position, is a slotted location bushhaving a shape and configuration as illustrated in FIG. 10. Forconvenience of reference, the location bush illustrated in FIG. 10 isgiven the reference numeral of 10-100. The slotted location bush 10-100has a circular head 10-10. The circular head 10-10 defines anoval-conical depression 10-20. The oval-conical depression 10-20 isadapted to receive positioning pins 1-100 b and 3-50 b therein. Theoval-conical configuration of the depression 10-20 allows one degree offreedom for the pins 1-200 b and 3-50 b received therein. The axis offreedom is in the X-direction of FIG. 1A, that is, parallel to the widthof the printing system 1-1000 (i.e. parallel to a direction of printmedia propagation).

The slotted location bush 10-100, allows the front-left corner of theprint head chassis 1-10 one degree of freedom along the X-axis of FIG.1A, that is along the direction parallel to a width of the printingsystem 1-1000 (i.e. parallel to a direction of print media propagation),but consistently aligns the corner along the Z-axis, that is, normal toa width of the printing system 1-1000 (i.e. normal to a direction ofprint media propagation). This allows for some degree of variation inthe manufacture and/or location of the pins 1-100 b and 3-50 b and thepin bush 2-100 b. In this manner, consistent and stable support of theprint head chassis 1-20 and the maintenance chassis 1-80 is lesssensitive to the exactness of manufacture and location of thepositioning pins 1-100 b and 3-50 b, and the pin bush 2-100 b.

The location bush 10-100, which allows for no freedom of movement in theX-Y plane for the positioning pins 1-100 a and 3-50 a received therein,hence determines the base/reference location of the print head chassis1-10 with respect to the platen 1-70 and the maintenance chassis 1-80.Together with the slotted location bush 10-100, which allows freedom ofmovement along the X axis but not the Z axis, and combined with the factthat the print head chassis 1-10 is a rigid structure, consistentalignment of the print head chassis 1-10 in the X-Z plane is achieved.The remaining two corners of the print head chassis 1-10 and themaintenance chassis 1-80 are positioned with respect to the positioningdetermined by the location bush 9-100 and slotted location bush 10-100.

The pin bushes 2-100 c and 2-100 d located at a rear-left and rear-rightunder-corners of the print head chassis 1-10 are flat pin bushes havinga shape and configuration as illustrated in FIG. 11. For convenience ofreference, the flat pin bushes illustrated in FIG. 11 is given thereference numeral of 11-100. The flat pin bush 11-100 has a circularhead 11-10, but unlike the location bush 9-100 and the slotted locationbush 10-100, does not have a depression defined into a top of the head11-10. Instead, the head 11-10 presents a solid, flat surface 11-20. Thehead 11-10 of the flat pin bush 11-100 used on the print head chassis asrear-left and rear-right bushes 2-100 c, 2-100 d may be formed with aflat head as opposed to a depression because further positioning of theprint head chassis 1-10 with respect to the platen 1-70 or to themaintenance chassis 1-80 is not necessary. The location bush 9-100 andthe slotted location bush 10-100 provide all necessary alignment of theprint head chassis 1-10 with respect to the platen 1-70 and themaintenance chassis 1-80.

Second Embodiment

FIG. 20 illustrates a print head chassis 1-10 according to a secondembodiment of the present invention. In the second embodiment, theventilation outlets 2-30 a, 2-30 b, 2-30 c, 2-30 d (see FIG. 2C) feedinto a pair of common aerosol extraction rails 20-10 a, 20-10 b viaconnectors 20-20 a, 20-20 b, 20-20 c, 20-20 d. The common aerosolextraction rails 20-10 a, 20-10 b feed into the aerosol filter 2-20.

The use of the common aerosol extraction rails 20-10 a, 20-10 beliminates the need for individual hoses connecting each of theventilation outlets 2-30 a, 2-30 b, 2-30 c, 2-30 d, 2-30 e, 2-30 f tothe aerosol filter 2-20. The print head chassis 1-10 is rendered lesscluttered, and permits easier user access to and manipulation of theelements supported in the print head chassis 1-10. Moreover, ventilationof the print head chassis 1-10 is noticeably improved.

Third Embodiment

FIGS. 21 and 21A illustrates a third embodiment of the presentinvention. In the third embodiment, the print head chassis 1-10 isprovided with support arms 21-10 a, 21-10 b, 21-10 c, 21-10 d. Supportarms 21-10 a, 21-10 b, 21-10 c, 21-10 d are attached respectively ateach corner of the print head chassis 1-10.

Each support arm 21-10 a, 21-10 b, 21-10 c, 21-10 d is respectivelyfixed to a corner of the print head chassis 1-10 and extends above theprint head chassis 1-10 in a crane-like manner, so as to overhang theedges of the print head chassis 1-10. Each support arm 21-10 a, 21-10 b,21-10 c, 21-10 d defines a support fixture 21-15 a, 21-15 b, 21-15 c,21-15 d at which there is provided a positioning pin 1-100 a, 1-100 b,1-100 c, 1-100 d. The positioning pins 1-100 a, 1-100 b, 1-100 c, 1-100d are each engaged with pin height adjusters 21-20 a, 21-20 b, 21-20 c,21-20 d which adjust the amount by which each positioning pin 1-100 a,1-100 b, 1-100 c, 1-100 d protrudes from the support fixtures 21-15 a,21-15 b, 21-15 c, 21-15 d.

In the third embodiment, the print head chassis 1-10 is supported from apair of gantries 21-30 a, 21-30 b via the positioning pins 1-100 a,1-100 b, 1-100 c, 1-100 d of the support arms 21-10 a, 21-10 b, 21-10 c,21-10 d. The gantries 21-30 a, 21-30 b are provided running above andacross the platen 1-70 to provide a framework suspended over the platen1-70 upon which the printing system 1-1000 is supported The gantries21-30 a, 21-30 b may be provided as part of the printing system 1-1000,or may be provided by 3^(rd) party providers to suit specificrequirements.

The printing system 1-1000 of the third embodiment includes a mountingframe 21-40 a, 21-40 b secured to the printer main frame 1-50. Eachmounting frame 21-40 a, 21-40 b includes a pair of pin bushes 2-100 a,2-100 b, 2-100 c, 2-100 d. The pin bushes 2-100 a, 2-100 b, 2-100 c,2-100 d provided on each mounting frame 21-40 a, 21-40 b are identicalto those used in the first embodiment. The mounting frame 21-40 a, 21-40b allows the printing system 1-1000 to be supported on the gantries21-30 a, 21-30 b, for example by way of a complementary ridge and groovecoupling between the mounting frame 21-40 a, 21-40 b and the gantries21-30 a, 21-30 b.

Similar also to the first embodiment is the use of a first pin bush witha circular-conical depression 9-20 as one of the pin bushes, the use ofa second pin bush with an oval-conical depression 10-20 as a second ofthe pin bushes, and the use of flat pin bushes with no depression as thethird and fourth of the pin bushes.

The pin bushes 2-100 a, 2-100 b, 2-100 c, 2-100 d provided on themounting frame 21-40 a, 21-40 b of each gantry 21-30 a, 21-30 b receivethe positioning pins 1-100 a, 1-100 b, 1-100 c, 1-100 d of the supportarms 21-10 a, 21-10 b, 21-10 c, 21-10 d in like manner to that describedin the first embodiment to provide consistent and stable support for theprint head chassis 1-10 with respect to the platen 1-70. Pin heightadjuster 21-20 a, 21-20 b, 21-20 c, 21-20 d allow the amount by whicheach positioning pin 1-100 a, 1-100 b, 1-100 c, 1-100 d protrudes to beadjusted, thereby allowing the height of the print head chassis 1-10with respect to the platen 1-70 to be adjusted.

In the first embodiment, the print head chassis 1-10 is supported onpositioning pins protruding upwards from the platen 1-70. Havingpositioning pins protruding from the platen 1-70 restricts the width ofthe print media upon which the printing system 1-1000 can print, sinceany print media that is used must fit within the bounds of theprotruding positioning pins.

In contrast, the third embodiment supports the print head chassis 1-10from gantries that are suspended above the platen 1-70. In this manner,the platen 1-70 is free of protrusions which limit the width of theprint media passing thereon. The printing system 1-1000 of the thirdembodiment therefore supports printing on print media of any width.

The third embodiment allows for the use of multiple printing systems1-1000 arranged on a plurality of gantries to span a wide-format printmedia web. Each gantries 21-30 a, 21-30 a is provided with a pair ofpositioning grooves 21-50 a, 21-50 b which respectively couple with acorresponding ridge on the mounting frames 21-40 a, 21-40 b of twoadjacent printing systems 1-1000. In this manner, multiple printingsystems 1-1000 are arranged side-by-side, and preferably offset witheach other, across a width of the print media to enable printing on awide-format print media.

The third embodiment therefore allows print media of any width to beemployed, requiring only sufficient printing systems 1-1000 to bemodularly arranged to span the width of the print media on anappropriate gantry framework.

Fourth Embodiment

FIGS. 22 to 24 illustrate a platen 1-70 according to a fourth embodimentof the present invention. The platen 1-70 of the fourth embodimentutilizes springs 22-10 (see FIG. 24) to bias positioning pins 1-100 a,1-100 b, 1-100 c, 1-100 d upwards, and utilizes clamping plates 22-20and clamping screws 22-30 to clamp the positioning pins 1-100 a, 1-100b, 1-100 c, 1-100 d at a suitable height.

The use of independent spring biased positioning pins 1-100 a, 1-100 b,1-100 c, 1-100 d at each corner of the platen 1-70 allows the height ofeach positioning pin 1-100 a, 1-100 b, 1-100 c, 1-100 d to be adjustedindependently of the other positioning pins. The balance and spacing ofthe print head chassis 1-10 from the platen 1-70 can therefore beflexibly adjusted to account for manufacturing tolerances, environmentalfactors, and the like to achieve an ideal spacing.

Moreover, the clamp and spring arrangement of each positioning pin 1-100a, 1-100 b, 1-100 c, 1-100 d of the fourth embodiment is mechanicallysimpler than the cammed system of the first embodiment, involving lessmechanical parts and movement and greater flexibility.

A desired height for each positioning pin 1-100 a, 1-100 b, 1-100 c,1-100 d is obtained by allowing each spring 22-10 to bias a respectivepositioning pin 1-100 a, 1-100 b, 1-100 c, 1-100 d upwards to thedesired height, and then clamping the clamping plates 22-20 against thepositioning pin 1-100 a, 1-100 b, 1-100 c, 1-100 d to lock thepositioning pin 1-100 a, 1-100 b, 1-100 c, 1-100 d in place at thedesired height.

Fifth Embodiment

FIGS. 25 and 26 illustrates an ink drainage system of the printingsystem 1-1000 according to a fifth embodiment of the present invention.According to the fifth embodiment, the ink collection channel 3-60 (seeFIG. 4C) of the maintenance chassis 1-80 is provided with a drainageport 25-10. Further, the waste ink tank 6-30 of the first embodiment isreplaced with a flat waste ink tray 25-20 provided on a base of theprinting system 1-1000. The flat waste ink tray 25-20 is lined with anabsorbent material 25-30 to capture the waste ink.

The flat waste ink tray 25-20 is sized to ensure that regardless of thepositioning of the maintenance chassis 1-80 (for example, whether theprinting system is in the printing position, transition position, ormaintenance position), the flat waste ink tray 25-20 captures ink fromthe drainage port 25-10.

In using a flat waste ink tray 25-20, the printing system 1-1000 is madeshorter in height, and more important, has no components which extendbelow the print head tiles 12-10 of the print head cartridges 1-20 a,1-20 b, 1-20 c, 1-20 d, 1-20 e. That is, the print head tiles 12-10 fromwhich ink is ejected are effectively the lowest, or equal lowest, pointof the printing system 1-1000 and are closest, or equal closest, to theplaten 1-70, in contrast with the embodiment illustrated in FIG. 6, forexample, where the waste ink tank 6-30 is substantially below a surfaceof the platen 1-70.

The above arrangement and utilization of the flat waste ink tray 25-20allows the printing system 1-1000 to be entirely supported/suspendedabove the platen 1-70 and used with print media of a platen that iswider than the printing system 1-1000 itself (as described in the thirdembodiment). This is in contrast to the printing system illustrated inFIG. 6, where it is clear that a platen that were to extend further inthe negative Z-direction (as defined by the axis in FIG. 1A) would notbe usable with the printing system as such a platen would be blocked andinterfered with by the waste ink tank 6-30.

It would be understood that the printing system 1-1000 of the firstembodiment, in having a waste ink tank and other components that aresubstantially lower than the print head chassis 1-10 in the printingposition, prevents the printing system 1-1000 from being entirelysuspended above the platen 1-70, and hence prevent the printing system1-1000 from being used with multiple printing systems 1-1000side-by-side to print on print media wider than the printing system1-1000.

In contrast, the printing system 1-1000 of the fifth embodiment has nocomponent protruding beyond the print head tiles 12-10 towards theplaten 1-70, and may therefore be positioned in any location/positionabove a platen of any size.

The flat waste ink tank 25-20 is sized to preferably match a footprintof the maintenance chassis 1-80. At a minimum, the flat waste ink tray25-20 is sized and shaped so as to have a portion thereof always underthe drainage port 25-10, regardless of the position the maintenancechassis 1-80 is currently in (e.g. storage position, operationalposition, or in between a storage and operational position). The sizeand shape of the flat waste ink tray 25-20 must therefore cover at leasta locus of movement of the drainage port 25-10 as the maintenancechassis 1-80 moves between the operational and storage port.

Mechanical Operation

An exemplary operation of the printing system 1-1000 is described withreference to FIGS. 1A to 1C.

Referring first to FIG. 1C, the printing system 1-1000 is illustrated inthe maintenance position. In the maintenance position, the print headchassis 1-10 is supported on the maintenance chassis 1-80. Specifically,the pins 3-50 a, 3-50 b, 3-50 c, 3-50 d located at the four corners onthe top of the maintenance chassis 1-80 support the location bush 2-100a, the slotted location bush 2-100 b, and flat pin bushes 2-100 c, 2-100d respectively. In this position, the print head cartridges 1-20 a-e areengaged with either the cappers 3-25 or the cleaners 3-27 of themaintenance chassis 1-80.

When the printing system 1-1000 is inactive, the print head cartridges1-20 a-e are preferably engaged with the cappers 3-25 to prevent theprint head cartridges 1-20 a-e from drying out and collectingcontaminants, and to generally prevent damage thereto. In order todisengage the print head cartridges 1-20 a-e from the cappers 3-25 andto instead engage the print head cartridges 1-20 a-e with the cleaners3-27 (or vice versa), the print head chassis 1-10 is first liftedupwards in the Y-direction by the lift mechanism 1-60 to a height, forexample, of that of the transition position illustrated in FIG. 1A. Withthe print head cartridges 1-20 a-e disengage from the cappers 3-25, thesub-frame movement mechanism 3-40 translates the maintenance chassissub-frame 3-10 in the X-direction, such that the cappers 3-25 are movedout of alignment with the print head cartridges 1-20 a-e and thecleaners 3-27 are moved into alignment with the print head cartridges1-20 a-e. The print head chassis 1-10 is then lowered back onto themaintenance chassis 1-80 into the maintenance position illustrated inFIG. 1C.

As the print head chassis 1-10 is lowered onto the maintenance chassis1-80, the location bush 2-100 a on the front-right under-corner of theprint head chassis 1-10 comes into contact with the pin 3-50 a on afront-right upper-corner of the maintenance chassis 1-80. Thecircular-conical depression 9-20 of the location bush 2-100 a receivesthe pin 3-50 a, and in doing so aligns the front-right corner of theprint head chassis 1-10 with respect to the maintenance chassis 1-80along the X-axis and Z-axis.

Similarly, the slotted location bush 2-100 b on the front-leftunder-corner of the print head chassis 1-10 comes into contact with thepin 3-50 b on the front-left upper-corner of the maintenance chassis1-80. The oval-conical depression 10-20 of the slotted location bush2-100 b receives the pin 3-50 b, and in doing so aligns the front-leftcorner of the print head chassis 1-10 with respect to the maintenancechassis 1-80 along the Z-axis. The front-left corner of the print headchassis 1-10 is already aligned along the X-axis by virtue of thelocation bush 2-100 a being fixed in the X-Z plane, and further byvirtue of the fact that the print head chassis 1-10 is a rigidstructure.

With the front-right and front-left corners of the print head chassis1-10 aligned and fixed along the X and Z axes, the print head chassis1-10 as a whole, in being a rigid structure, is aligned with themaintenance chassis 1-80. Flat bushes 2-100 c and 2-100 d at therear-left and rear-right lower corners of the print head chassis 1-10may be simply supported by pins 3-50 c and 3-50 d respectively of theprint head maintenance chassis 1-80 without requiring locationslots/depressions such as present in location bush 2-100 a and slottedlocation bush 2-100 b.

With the print head chassis 1-10 again supported by the maintenancechassis 1-80, but with the maintenance chassis 1-80 now having moved themaintenance chassis sub-frame 3-10 so as to move the cappers 3-25 out ofalignment with the print head cartridges 1-20 a-e and the cleaners 3-27into alignment with the print head cartridges 1-20 a-e, the print headcartridges 1-20 a-e are positioned in contact with respective firstrollers 3-29 of the cleaners 3-27, which first rollers 3-29 are made ofthe microfiber material for wiping across a print head of the print headcartridges 1-20 a-e.

To transition the print head chassis 1-10 from the maintenance positionto the printing position, the maintenance chassis 1-80 needs to beretracted into the printer main frame 1-50 and the print head chassis1-10 accurately lowered and positioned with respect to the platen 1-70.Accordingly, the print head chassis 1-10 is first lifted by the liftingmechanism 1-60 to the transition position illustrated in FIG. 1A.

At the transition position, the print head chassis 1-10 is not supportedby the maintenance chassis 1-80, and the print head cartridges 1-20 a-eare disengage from the maintenance cradles 3-20 a-e. The maintenancechassis 1-80 is hence free to be retracted back into the printer mainframe 1-50, as shown in FIG. 1B.

With the maintenance chassis 1-80 retracted back into the printer mainframe 1-50, the printer head chassis 1-10 is free to be lowered towardsthe platen 1-70. Accordingly, the lifting mechanism 1-60 lowers theprint head chassis 1-10 towards the platen 1-70.

In the first embodiment of the printing system, as the print headchassis 1-10 approaches the platen 1-70, the location bush 2-100 a onthe front-right bottom corner of the print head chassis 1-10 comes intocontact with the pin 1-100 a on a front right corner of the platen 1-70.In a similar manner to that described above with regards to thealignment of the print head chassis 1-10 with the maintenance chassis1-80, the print head chassis 1-10 is aligned to the platen 1-70 by thereceipt of the pin 1-100 a into the circular-conical depression 9-20 ofthe locating bush -200 a. In this manner, the front-right corner of theprint head chassis 1-10 is aligned with respect to the platen 1-70 alongthe X-axis and Z-axis.

Similarly, the slotted location bush 2-100 b on the front-left bottomcorner of the print head chassis 1-10 comes into contact with the pin1-100 b on the front-left upper corner of the platen 1-70. Theoval-conical depression 10-20 of the slotted locating bush 2-100 breceives the pin 1-100 b, and in doing so aligns the front-left cornerof the print head chassis 1-10 with respect to the platen 1-70 along theZ-axis. The front-left corner of the print head chassis 1-10 is alreadyaligned along the X-axis by virtue of the location bush 2-100 a beingfixed in the X-Z plane, and further by virtue of the fact that the printhead chassis 1-10 is a rigid structure.

With the front-right and front-left corners of the print head chassis1-10 aligned and fixed along the X and Z axes, the print head chassis1-10 as a whole, in being a rigid structure, is aligned with the platen1-70. Flat bushes 2-100 c and 2-100 d at the rear-left and rear-rightlower corners of the print head chassis 1-10 may be simply supported bypins 1-100 c and 1-100 d respectively of the platen 1-70 without needfor locating slots/depressions such as those defined in locating bush2-100 a and slotted locating bush 2-100 b.

The pins 1-100 a, 1-100 b, 1-100 c, 1-100 d, of the platen 1-70, and thepins 3-50 a, 3-50 b, 3-50 c, 3-50 d, of the maintenance chassis 1-80,and the location bush 2-100 a, slotted location bush 2-100 b, and flatbushes 2-100 c, 2-100 d, in all being fabricated from a rigid, hard anddurable material such as, for example, steel, ensure that accuratepositioning of the print head chassis 1-10 with respect to themaintenance chassis 1-80 and platen 1-70 is consistently, and repeatedlyattained.

In particular, the spacing between the print head cartridges 1-20 a-eand the platen 1-70 is consistently achieved despite repeated movementof the print head chassis 1-10 towards and away from the platen 1-70.Similarly, alignment of the print head cartridges 1-20 a-e with respectto the maintenance cradles 3-20 a-e is also consistently achieveddespite repeated movement of the print head chassis 1-20 towards andaway from the maintenance chassis 1-80, and movement of the maintenancechassis 1-80 to and from a retracted position within the printer mainframe 1-50.

Moreover, the relative spacing between the print head cartridges 1-20a-e is kept consistent since the print head cartridges 1-20 a-e are notmoved with respect to each other. Rather, the print head cartridges 1-20a-e are moved as a unitary set by moving the print head chassis 1-10.The same applies to the maintenance cradles 3-20 a-e, in being moved asa unitary set by moving the maintenance chassis 1-80 rather thanindividual cradles 3-20 a-e.

Any loss of accuracy and consistency in the alignments of the print headchassis 1-10, maintenance chassis 1-80, and platen 1-70 with respect toeach other is caused mainly by a wearing of the positioning pins 1-100a, 1-100 b, 1-100 c, 1-100 d, 3-50 a, 3-50 b, 3-50 c, 3-50 d and bushes2-100 a, 2-100 b, 2-100 c, 2-100 d. In view, however, that suchcomponents are fabricated from a hard, durable, and rigid material suchas steel, and that the movements of the print head chassis 1-10 andmaintenance chassis 1-80 with respect to each other and the platen 1-70are performed in a relatively concise and gentle manner, the wearing ofsuch components is not considered an issue over the lifetime of theprinting system 1-1000.

The mechanical operation of the printing system 1-1000 according to thethird embodiment, in which support arms 21-10 a, 21-10 b, 21-10 c, 21-10d support the print head chassis 1-10 on gantries 21-30 a, 21-30 binstead of the print head chassis 1-10 being supported on the platen1-70, is similar to that described above for the first embodiment.

In the third embodiment, the print head chassis 1-10 is lowered untilthe positioning pins 1-100 a, 1-100 b, 1-100 c, 1-100 d of each supportarm 21-10 a, 21-10 b, 21-10 c, 21-10 d are received by the pin bushes2-100 a, 2-100 b, 2-100 c, 2-100 d on the mounting frames 21-40 a, 21-40b. The interaction of the positioning pins 1-100 a, 1-100 b, 1-100 c,1-100 d with the pin bushes 2-100 a, 2-100 b, 2-100 c, 2-100 d isidentical to that described above for the mechanical operation of thefirst embodiment. Additionally, pin height adjusters 21-20 a, 21-20 b,21-20 c, 21-20 d may be manipulated as necessary to adjust the height ofthe print head chassis 1-10 from the platen 1-70 at each corner

System Alignment

In a printing system utilizing multiple, spaced-apart print heads, andin particular a printing system in which the multiple, spaced-apartprint heads are required to eject ink drops in very close vicinity (andpreferably directly on top) of a dot ejected by another print head,consistency of positioning between the various hardware components suchas the platen, the print head cartridges, and between the print headcartridges themselves, is necessary to achieve high print quality.

The above described printing system 1-1000 provides for the movement ofprint head cartridges as necessary to effect maintenance, sealing, andoperation of the print head cartridges whilst maintaining consistency ofpositioning between print head cartridges and between the print headcartridges and other components of the printing system such as theplaten and print media. However, whilst the above described printingsystem 1-1000 is able to maintain the necessary alignments betweenvarious components despite repeated movement of the various components,the various components need to first be properly aligned.

The use of multiple, spaced-apart print heads which each print a singlecolour, however, introduces challenges to achieving proper alignmentthat single print head systems and systems utilizing a scanning-typeprint head do not encounter. The challenges of alignment are describedin greater detail below.

The printing system 1-1000 of the present disclosure utilizes multipleprint head cartridges 1-20 a-e, each printing a single colour. Eachprint head cartridge 1-20 a-e is separated from a neighbouring printhead cartridge in the direction of print media propagations (i.e. X-axisin FIG. 1A) and by a distance that is significantly larger than a widthof a nozzle or a dot pitch. This distance is measurable in centimetres,and in one embodiment, the print head cartridges 1-20 a-e have aseparation pitch of around 8 centimetres.

One print head cartridge 1-20, as shown in FIG. 12 and as previouslydescribed, comprises of a number of print head tiles arranged end to endto span the width of the print media. In FIG. 12, the print headcartridge 1-20 is exemplarily illustrated with 11 print head tiles 12-10arranged end to end. Each print head tile has a number of logical rows12-20 of nozzles. In FIG. 12, each print head tile 12-10 is exemplarilyillustrated with 5 logical rows of nozzles. In contrast to a singleprint head cartridge (SPHC) system, all of the 5 logical rows of nozzleseject the same coloured ink. Each logical row of nozzles is separatedinto a pair of sub-rows 12-30, 12-40, one sub-row for printing even dotsand the other sub-row for printing odd dots. Whilst FIG. 12 shows onelogical row 12-20 as being comprised of two adjacent sub-rows 12-30,12-40, a logical row may in fact be comprised of any even dot printingsub-row 12-30 and any odd dot printing sub-row 12-40, not necessarilyadjacent to each other.

In the printing system 1-1000, a nozzle of one logical row of one printhead tile has to eject a drop of ink in very close vicinity (andpreferably on top) of a corresponding nozzle of a corresponding row of acorresponding print head tile of another print head cartridge that maybe around 32 cm away.

Similar to systems employing a single, pagewidth print head cartridge(SPHC), a multiple print head cartridge (MPHC) system must ensure thatthe print head tiles making up each print head cartridge are inalignment with each other. However, in addition to the need to aligneach of print head tiles of one print head cartridge, there is further aneed to align each print head cartridge with the other print headcartridges, and still further align each print head tile of one printhead cartridge with the other print head tiles of the other print headcartridges that are in the same line up/downstream along a direction ofprint media propagation.

Moreover, it has been found that print media that is being propagatedacross the paper shifts and wobbles. In an SPHC system, this shiftingand wobbling of the print media was not realized, or ignored, since apossible amount of aberrant print media movement from the time the printmedia passes under a first nozzle row to the time it passes under a lastnozzle row is small, if not negligible. Similarly, in a scanning-typesystem, the swathes printed by each scan iteration are relatively small,and a possible amount of aberrant print media movement in the distancethe print media is moved from a first swathe to the next is small, ifnot negligible. The positioning of the print media with respect to theprint head cartridge in an SPHC system and a scanning-type system, fromthe perspective of the nozzles, can therefore be seen as relativelyconsistent.

In the printing system 1-1000 of the present disclosure, however, theshifting and wobbling of the print media become significant and requirenon-trivial compensation, since a first print head cartridge may beseparated from the last print head cartridge by around 32 cm. The amountof possible aberrant print media movement as the print media ispropagated a distance of 32 cm is quite significant.

A view of the print media as seen by a nozzle printing Cyan in a Cyanprint head cartridge may be vastly different to a view of the printmedia seen by a nozzle printing Yellow in the Yellow print headcartridge, which could be around 32 centimetres away. Ashifting/wobbling of the print media as the print media is fed along theplaten, which conventionally can be ignored due to either the closenessof the different coloured nozzles (for an SPHC system) or the smalldistance the paper moves between printing of swathes (for ascanning-type system), can no longer be ignored.

To firstly address the issue of alignment between one print head tile ofone print head cartridge and the other print head tiles of the otherprint head cartridges that are in the same line up/downstream along adirection of print media propagation, a 2-D Vernier calibration methodis performed.

FIG. 13 illustrates a 2-D Vernier calibration map 13-100 according to onembodiment of the present disclosure. The 2-D Vernier calibration map13-100 comprises rows 13-50, 13-60, 13-70, 13-80 of horizontally printedVernier patterns 13-10 printed across the map. The 2-D Verniercalibration map 13-100 further includes a row 13-90 of verticallyprinted Vernier patterns 13-20 printed along the bottom of the map. Asolid colour bar 13-30 may be printed at a top of the map to help ensureproper priming of the print head cartridges 1-20 a-e.

Each horizontally printed Vernier pattern 13-10 comprises twooverlapping patterns, one printed by a print head tile of a referenceprint head cartridge and the other printed by a print head tile ofanother (a comparison) print head cartridge. For purposes of thefollowing description, the Black print head cartridge is used as thereference print head cartridge. It should be understood that any one ofthe print head cartridges 1-20 a-e may alternatively be used as thereference print head cartridge.

The first row 13-50 of the Vernier calibration map 13-100 illustratesVernier patterns 13-10 comprising of 11 patterns printed by the Blackprint head cartridge overlapped with 11 patterns printed by the Cyanprint head cartridge. The number of Vernier patterns 13-10 printed ineach row 13-50, 13-60, 13-70, 13-80 is not limited to 11, butpreferably, at least one Vernier pattern is printed for each print headtile 12-10 making up a print head cartridge 1-20.

The position of a dense region 13-110 in each horizontally printedVernier pattern 13-10 indicates a relative vertical misalignment betweenthe print head tiles that were involve in the printing of a given scale.For example, if the Cyan print head cartridge is ideally exactly 8 cmfrom the reference Black print head cartridge, a 2-D Vernier calibrationmap 13-100 set up to measure this ideal will show a dense region 13-110around the middle of each horizontally printed Vernier pattern 13-10 inthe first row 13-50 if the Cyan print head tiles of the Cyan print headcartridge are indeed all exactly 8 cm away from the Black print headtiles of the reference Black print head cartridge.

If the first row 13-50 of the Vernier calibration map 13-100 shows afirst horizontal Vernier pattern having a dense region 13-110 near abottom of the scale, this would indicate that the left-most Cyan printhead tile is further than 8 cm from a corresponding Black print headtile. If this dense region 13-110 gradually moves higher up the scalefor each subsequent Vernier horizontally printed scale in the first row13-50, it may indicate that the Cyan print head cartridge as a whole isdiagonally skewed with respect to the Black print head cartridge. Othersimilar conclusions can be drawn from the positions of the dense regions13-110 relative to other dense regions 13-110 in the Vernier calibrationmap 13-100. Included in such conclusions are recognizing when only oneprint head tile is misaligned, whereas the remaining print head tiles ofa print head cartridge are otherwise sufficiently aligned, recognizingwhen an entire print head cartridge as a whole is misaligned,recognizing when a print head cartridge is structurally/mechanicallybowed, and the like.

Analysis of the alignments of the other print head cartridges withrespect to the reference print head cartridge is made by referring inidentical fashion to the remaining rows 13-60, 13-70, 13-80 of theVernier calibration map 13-100.

FIG. 14 schematically illustrates in detail the components of eachhorizontally printed Vernier pattern 13-10. As shown in illustration (a)of FIG. 14, each horizontally printed Vernier pattern 13-10 is made upof a reference pattern 14-10 printed by the reference print headcartridge (shown as the pattern of dark/black lines) and a comparisonpattern 14-20 printed by a comparison print head cartridge (shown as thepattern of lighter/grey lines).

Illustrations (b), (c) and (d) of FIG. 14 show the two patternsoverlapping. For purposes of clarity, and ease of description,illustrations (b), (c), and (d) schematically show the reference patternonly partially overlapping the comparison pattern in a horizontaldirection. In practice, both the reference and comparison patterns arefully overlapping such that the left and right edges of both patternsare aligned with each other, as shown in FIG. 13. The reference patternis printed with a different vertical pitch from the comparison pattern,in accordance with the Vernier method. This produces an interferencepattern as shown in illustrations (b), (c) and (d), which can be used toindicate the misalignment of the print head tiles that were involved inthe printing of the pattern.

Illustration (b) illustrates a pattern where the comparison print headtile is accurately positioned with respect to the reference print headtile. If the Vernier calibration map 13-100 is set up for a system inwhich the print head cartridges are ideally multiples of 8 cm from thereference print head cartridge, then illustration (b) showing the denseportion 13-110 in the middle of the interference pattern indicates thatthe comparison print head tile that printed the grey pattern is ideallypositioned.

Illustration (c) illustrates a pattern where the comparison print headtile is slightly lower or further than the ideal separation from thereference print head tile. In Illustration (c), the dense portion 13-110is nearer to a bottom of the interference pattern.

Illustration (d), at first glance, illustrates a pattern suggesting thatthe comparison print head tile is higher or nearer than the idealseparation from the reference print head tile. However, coarse alignmentsquares 14-30 printed at the top of the pattern indicate that in actualfact, the comparison print head tile is very much lower or further thanthe ideal separation from the reference print head tile. Such an extremeseparation causes the interference pattern to “wrap” around and appearat the top of the pattern.

By referring to the interference pattern formed for each row 13-50,13-60, 13-70, 13-80 of the Vernier calibration map 13-100, an alignmentalong the direction of print media propagation (i.e. X-axis of FIG. 1A)of each print head tile of each print head cartridge with respect to areference print head cartridge can be determined Any misalignments thusdetermined are accounted for, if necessary, by physically adjusting thepositioning of a print head cartridge and/or manipulating the print datato be sent to the print head cartridge. In particular, the interferencepatterns shown by the Vernier horizontally printed scales 13-10 can beused to determine if a print head cartridge as a whole is misalignedwith respect to the reference print head cartridge, or if it is just oneprint head tile of either the reference or comparison print headcartridge that is misaligned with everything else.

In this manner, the relative positions of each print head tile along adirection of print media propagation (i.e. X-axis of FIG. 1A) may beadjusted as necessary with respect to a corresponding reference printhead tile.

The vertically printed Vernier pattern 13-20 is used for a similarpurpose to that of the horizontally printed Vernier pattern 13-10. Thevertically printed Vernier pattern 13-20 illustrates a horizontal (i.e.Z-axis of FIG. 1A) misalignment of one print head tile with respect to acorresponding print head tile of the reference print head cartridge.

Ideally, a print head tile of a comparison print head cartridge that islinearly upstream or downstream of a print head tile of the referenceprint head cartridge is exactly in line with a corresponding print headtile of the reference print head cartridge. That is, a first nozzle of afirst print head tile of the comparison print head cartridge is ideallycollinear with a first nozzle of a first print head tile of thereference print head tile, along a direction of print media propagation(i.e. X-axis of FIG. 1A).

It is unavoidable, however, that the print head tiles of the print headcartridges are not always so perfectly align, and are instead spacedaway from the ideal line. If the X-axis indicates an imaginary linealong which the first nozzle of the first print head tile of all printhead cartridges should ideally be exactly positioned, and if thisimaginary line is drawn from the top to bottom of this page, the nozzlesof the print head cartridges are often found slightly left or right ofthis imaginary line.

The vertically printed Vernier pattern 13-20 is used to indicatemisalignment in this direction. If a comparison print head tile isperfectly aligned with the reference print head tile, that is, if allnozzles of the comparison print head tile are perfectly collinear withcorresponding nozzles of the reference print head tile along the X-axis,a dense region 13-120 is formed in the middle of the interferencepattern of the vertically printed Vernier pattern 13-20. Variation ofthe comparison print head tile to the left or right (i.e. negative orpositive Z-axis direction of FIG. 1A) relative to the reference printhead tile will appear as a shift in the position of the dense region inthe interference pattern of the vertically printed Vernier pattern13-20. The vertically printed Vernier pattern 13-20 also includes coarsealignment squares 14-40 serving a similar purpose to the coarsealignment squares 14-30 of the horizontally printed Vernier pattern, butin a horizontal direction.

Apart from physically re-aligning print head cartridges, compensationfor misalignment of print head tiles with corresponding reference printhead tiles is also achieved by vertically and horizontally shifting dotdata sent to the print head cartridges. Since the misalignment of oneprint head tile with the reference print head tile does not generallychange over time so long as the same print head cartridges are beingused, compensation for this misalignment may be performed as a once-offor infrequent event. The amount of compensation needed for each printhead cartridge can therefore be statically stored in a memory of arespective print head controller module. A method of shifting dot datato compensate for misalignment of print head tiles is described indetail later below.

Recalibration of the print head cartridges is preferably performedanytime one or more of the print head cartridges is replaced. Print headcartridges may be replaced as a result of wear and tear, maintaining acertain print quality, changing ink ‘colours’, and so forth.

As mentioned above, in a printing system comprising multiple print headcartridges, and where the print head cartridges are spaced apart fromeach other by a relatively great distance (e.g. a distance far greaterthan a nozzle width or dot pitch, and a distance measurable in one ormore whole units of centimetres) along a direction of print mediapropagation, the view of the print media as seen by each print headcartridge at any given instant may be quite different from one printhead cartridge to the next due to a shifting and wobbling of the printmedia as it is propagated across the platen.

To address the issue of misalignment caused by a shifting/wobbling ofthe print media as the print media propagates past the print headcartridges 1-20 a-e, the printing system 1-1000 employs a vision system15-1000 (see FIG. 15) to track the shifting/wobbling of the print media.

In one embodiment, as illustrated in FIG. 15, the first print headcartridge 1-20 a prints a reference line of dots 15-10 along an edge ofthe print media, parallel to a direction of print media propagation. Asensor 15-20 is provided near each of the downstream print headcartridges 1-20 b, 1-20 c, 1-20 d, 1-20 e for detecting this referenceline of dots 15-10. The sensor includes a series of detectors Det_(—)1,Det_(—)2, Det_(—)3, Det_(—)4, Det_(—)5 positioned perpendicularly to thereference line of dots printed by the first print head cartridge 1-20 a.The shifting/wobbling of the print media is determined by determiningwhich detector of the series of detectors Det_(—)1, Det_(—)2, Det_(—)3,Det_(—)4, Det_(—)5 detects the reference line of dots 15-10.

For example, assume the sensor 15-20 provided with the five detectorsDet_(—)1, Det_(—)2, Det_(—)3, Det_(—)4, Det_(—)5 positioned in singlefile perpendicular to the reference line 15-10 of dots printed by thefirst print head cartridge detects the reference line of dots 15-10 atdetector Det_(—)3. This would indicate that the print media has notshifted/wobbled from the time it past under the first print headcartridge to its present position under the sensor. Or alternatively, itwould indicate that the print media has shifted/wobbled back to the sameposition as it had when passing under the first print head cartridge. Ifthis sensor were the sensor attached to the second print head cartridge1-20 b, then no compensation is necessary for the print data and firingsequence of the second print head cartridge.

Assume next that the sensor 15-20 attached to the third print headcartridge detects the reference line of dots 15-10 printed by the firstprint head cartridge via detector Det_(—)1. This would indicate that theprint media has shifted/wobbled in the Z-direction, using the axesdefined in FIG. 1A. Accordingly, the print data supplied to the thirdprint head cartridge needs to be shifted in the Z-direction tocompensate for this shifting/wobbling of the print media.

In the above manner, a dynamic compensation is achieved allowing for themultiple, spaced-apart print head cartridges 1-20 a-e to accuratelyeject dots on top (or in very close vicinity) of previously ejected dotsto achieve proper alignment of each monochrome image.

The reference line of dots 15-10 printed by the first print head 1-20 ais preferably invisible to human detection. For example, the referenceline 15-10 of dots is preferably printed using infrared ink, and thesensor 15-20 comprised of infrared detectors.

In another embodiment, the edge of the print media is detected and usedas a reference line. The edge of the print media is used in a similarmanner to that of the above embodiment to allow the subsequent,downstream print head cartridges to compensate for the shifting/wobblingof the print media. In this embodiment, each of the print headcartridges 1-20 a-e is provided with a sensor for detecting the edge ofthe print media. The first print head cartridge 1-20 a detects theposition of the edge of the print media and communicates this positionto the subsequent, downstream print head cartridges. The subsequent,downstream print head cartridges 1-20 b, 1-20 c, 1-20 d, 1-20 e eachdetect the position of the edge of the print media as the print mediapasses respectively under each print head cartridge, and compares thedetected position with the position detected by the first print headcartridge when that portion of the print media passed under the firstprint head cartridge.

The subsequent print head cartridges shift print data as necessary tocompensate for any difference in the detected edge of the print mediacompared to the edge detected by the first print head cartridge.

A benefit of detecting the edge of the print media compared to printinga reference line is that in detecting the edge of the print media, eachprint head cartridge is able to perform compensation on its own printdata relative to the absolute edge of the print media, to account forany shifting/wobbling of the print media. In contrast, the compensationmethod using a reference line printed by the first print head cartridgeassumes that the first print head cartridge is consistently aligned withrespect to the print media. In a case where this assumption is wrong,the image printed by print head cartridges 1-20 a-e will still bealigned respective to each other, but may not necessarily be aligned tothe print media itself. For example, a clear, high definition image willbe printed, but which image may wobble or be skewed relative to theprint media. A system in which the edge of the print media is detectedrequires, however, the use of high quality print media which has aconsistent edge.

Alternatively, a hybrid dynamic compensation system may be employed, inwhich a combination of detecting the edge of the print media andprinting of a reference line is used. The hybrid dynamic compensationsystem utilizes a print media edge detecting vision system for the printhead cartridge printing the reference line, and utilizes the referenceline vision detecting system as described above for the remaining printhead cartridges.

Print Data Preparation and Misalignment Compensation

With reference to FIGS. 16A to 16D, a process by which a colour image isprepared for printing by a computer system is described.

At step 16-10 illustrated in FIG. 16A, a colour image is firstlyprovided to a computer system. The colour image may, for example, be inan XPS or GDI page description language, as is common when working withMicrosoft™ applications.

At step 16-20 illustrated in FIG. 16B, the colour image is rasterized bythe computer system to obtain a bitmap of colour pixels. The bitmapdescribes the colour of each pixel in an image colour space, such as forexample RGB, sRGB, and the like. The colour of each pixel is representedas a combination of a set of base colours in certain proportions, forexamples 25% red, 32% green, 76% blue. The bitmap specificallyillustrated at step 16-20 describes the source image in R, G, B and aspot colour. For purposes of description, the spot colour is exemplarilytaken to be Khaki.

At step 16-30, the image colour space is converted to a printing colourspace for printing. The output of this step produces a bitmap where eachpixel is described by a number of values. Each value corresponds to anink ‘colour’ or type that the printing system 1-1000 prints. Forexample, if the printing system 1-1000 has been set up such that the 5print head cartridges respectively print Cyan, Magenta, Yellow, Black,and Spot-Khaki, the bitmap produced in 16-30 is in the 22-M-Y-K-SpKHcolour space and represents each pixel as an intensity of each of thesecolours, with the exception of Spot-Khaki. Spot colours, which are usedto print specific colours without combining inks, are binary inrepresentation and are either printed at a given location, or not.

As another example, the printing system 1-1000 may be set up to printSpot-Khaki, Spot-Blue, and Spot-Pink, with the 2 remaining print headcartridges unused. In this case step 16-30 converts the colour bitmapgenerated in step 16-20 into a SpKH-SpBL-SpPK colour space. Accordingly,the actual colour space of the printing colour space depends on thesetup of the printing system 1-1000 at any given time. It should bereadily understood that the printing system 1-1000 is not limited onlyto the colours and printing colour spaces described above, but may beset up to print any combination of colours as necessary.

For ease of description, it is assumed hereinbelow that the printingsystem 1-1000 has been set up to print Cyan, Magenta, Yellow, Black, andSpot-Khaki. The image colour space generated in step 16-20 is henceconverted into a 22-M-Y-K-SpKH colour space as the printing colourspace.

At step 16-40 illustrated in FIG. 16C, each of the colours of the22-M-Y-K-SpKH colour space is separated into separate colour planes.Each colour plane represents the original colour image as a monochromeimage containing only the colour of that plane.

At step 16-50, each monochrome image is dithered. This converts themonochrome image in which each pixel is represented by an intensity (orshade), to a binary image where each pixel is either on or off. Thecombination of on/off pixels in a small area approximates the intensity(or shade) of the original monochrome image. Additionally, the ditheringof any given pixel in one monochrome image may be influenced by thecorresponding pixels in the other monochrome images.

At step 16-60 illustrated in FIG. 16D, the dots of each monochromedithered image are sent to the print engines of corresponding print headcontroller modules as dot data. The dot data may be compressed beforebeing sent to the print engine. For example, the dots of the Cyandithered image may be sent to the first print head controller module1-25 a, the dots of the Magenta dithered image sent to the second printhead controller module 1-25 b, and so forth. FIG. 16D also schematicallyillustrates a delay added to some dithered images to account for thefact that the print heads are space apart along a length of the printmedia and hence should commence printing at different times.

FIGS. 17A and 17B illustrate the processing of the dot data sent to eachprint head controller module 1-25 a-e from the computer system in step16-60. Each print head controller module 1-25 a-e includes a printengine for further processing the dot data.

At step 17-10, the dot data generated at step 16-60 for a monochromedithered image is received in an input data buffer of a print engine ofa corresponding print head controller module 1-25 a-e. The dot data isreceived and decompressed if necessary, then placed in the input databuffer. Data from the input buffer is then separated into even dotscorresponding to dots to be ejected from even numbered nozzles, and odddots corresponding to dots to be ejected from odd numbered nozzles (step17-20). The even dots are received in an even bits buffer, and the odddots are received in an odd bits buffer. Each buffer hence holds halflines of data (i.e. all even bits of a line, or all odd bits of a line).

At step 17-30, vertical calibration is performed on the data in the evenbits buffer and the odd bits buffer. Data in each buffer is logicallygrouped into vertical calibration regions. Each vertical calibrationregion may be shifted up or down to effect any necessary verticalcompensation of the dot data. In FIG. 17A, vertical calibration region 1in both the even bits buffer and odd bits buffer is shown being shifteddown a line. The need to shift dot data in vertical calibration region 1down a line may be to, for example, compensate for a verticalmisalignment of a particular print head tile.

At step 17-40, illustrated in FIG. 17B, the dot data from both the evenbits buffer and the odd bits buffer is combined into an output buffer.The dot data from the even bits buffer and the odd bits buffer arecombined in an order to achieve an ordering of dots that takes intoaccount compensation for misalignment, the fact that not all nozzles ofa print head cartridge are fired simultaneously (for heat and electricalload reasons, amongst others), and other timing and firing sequenceissues.

The order of dots in the output buffer further takes into account thatthe first row of nozzles of a print head cartridge may be separated fromthe last row of nozzles by a significant number of dot pitches. In theprinting system 1-1000, a first row of nozzles is separated by 44 dotpitches from the last row of nozzles. Accordingly, the first row may beprinting data 44 lines ahead of the last row. The visual ordering of thedot data illustrated in the output buffer at step 17-40 is hence notreadily comprehensible to humans.

Further at step 17-40, horizontal compensation of the dot data toaccount for paper wobble, and misalignments between print headcartridges is also performed. As illustrated in FIG. 17B, a number ofrows are exemplarily shifted horizontally by 1 dot pitch to compensatefor paper wobble detected by the sensors 15-1000, and the like.

At step 17-50, further compensation is applied to the dot data in theoutput buffer to account for specific physical arrangements of the printhead cartridge, such as a drop triangle arrangement, and then the datais finally formatted into a format specific to the print head controllermodules and print heads, so as to be understood, read out, and executedappropriately. Included within this formatting may be inclusions ofnon-ejection firing pulses to maintain the nozzles of print head tilesat certain temperatures, “keep wet” firing patterns, dead nozzlecompensations, 8b10b encoding, interspersion of print commands and printdata, and the like.

The above described processing of print data is suitable for a printingsystem employing print engines designed to work with monochromepagewidth print head cartridges. However, as previously described,conventional page width print head cartridges used in colour printingsystems are not monochrome. Instead, a single pagewidth print headcartridge prints all colours, not just one.

The following describes a modification to the above processing of printdata that allows a multi-coloured pagewidth print head cartridge andcorresponding multi-coloured print engine to operate in monochrome in amultiple print head cartridge colour printing system such as theprinting system 1-1000. In this manner, existing multi-coloured pagewidth print head cartridges and corresponding multi-coloured printengines maybe be used in the printing system 1-1000, therebyameliorating the need to purchase new monochrome pagewidth print headcartridges and print engine, and accordingly saving costs.

A print engine that is originally designed to drive a multi-colouredprint head cartridge receives pixel data for a number of colour planes,and generates dot data for each colour plane. The dot data for eachcolour plane is sent to a specific row of nozzles on the one print headcartridge, and the specific row of nozzles timed to fire such that theink ejected by the specific row of nozzles lands on dots ejected by anupstream row of nozzles.

To cause a multi-coloured print engine and print head cartridge toinstead operate in monochrome, and further, to eject ink such that eachrow of nozzles ejects ink to a new line on a print media rather than ontop of a previously printed line, the monochrome pixel data sent to theprint engine has to be disguised as if it comprised of a number of‘colour’ planes, and the print media has to be made to propagate pastthe print head cartridge at a higher speed.

The above process is described with reference to FIGS. 18A, 18B and 19.At step 18-10, illustrated in FIG. 18A, image data representing a fullcolour source image is received by a computer system. For ease ofdescription, the image data shown at step 18-10 has already beenconverted to a printing colour plane (e.g. CMYK). If the image data hasnot already been converted to a CMYK colour plane, the steps asdescribed previously with regard to FIGS. 16A to 16D are executed toconvert the image data to a CMYK colour plane.

At step 18-20, the image data is separated by the computer system intoindividual colour planes to obtain monochrome images of the originalsource image. The steps so far are similar to those of 16-10 to 16-40.

At step 18-30, each individual colour plane is treated as if itrepresented a multi-coloured image. For ease of description, the processis described below with respect to the yellow colour plane, but itshould be understood that similar processes are performed for each ofthe other colour planes M, Y and K. The yellow colour plane is splitinto groups 18-100 of a number of vertical lines. In the embodimentillustrated by FIG. 18B, the yellow colour plane is split into groups18-100 of 3 vertical lines each. Each line in a group is pretended torepresent a different colour. For example, row 1 of each group may beconsidered as representing ‘pink’ data, row 2 as ‘lime’ data, and row 3as ‘orange data.

The number of vertical lines in a group determines (or depends on) thenumber of rows of nozzles that each print head cartridge uses (orneeds). Here, each group contains 3 vertical lines and therefore 3 rowsof nozzles will be used/needed. In the system of 1-1000, each print headcartridge has 5 rows of nozzles. Accordingly, 2 rows of nozzles will beunused and/or used for redundancy, for example, to compensate for deadnozzles in the other 3 rows or to increase the print density.

At step 18-40, the ‘pink’ lines (i.e. row 1) of each group 18-1000 arecombined to form a ‘pink’ fake colour plane. Similarly, the ‘lime’ linesand the ‘orange’ lines of each group are combined to respectively form a‘lime’ fake colour plane and an ‘orange’ fake colour plane. With thedata of the Yellow colour plane now separated into three fake colourplanes, the data from each of the three fake colour planes are combinedand formatted to look like image data having 3 colour planes (step18-50). This image data can be said to be in a P*L*O* colour space, thatis a fake Pink, fake Lime, fake Orange colour space. It should be pointout at this juncture that the image data in the P*L*O* colour space isstill in actuality data that represents only the yellow colour plane ofthe original source image. The image data in the P*L*O* colour space isthen sent to the multi-coloured print engine. The data may be compressedin some manner before being sent to the multi-coloured print engine.

FIG. 19 illustrates the processing of the image data in the P*L*O*colour space by a multi-coloured print engine that is expectingmulti-coloured data rather than monochrome data. At steps 19-10 and19-20, the multi-coloured print engine decompresses the print data ifnecessary, then performs multi-coloured processing on the receivedP*L*O* colour space image. Namely, the P*L*O* colour space image isseparated into a separate P* colour plane, L* colour plane, and O*colour plane. The data of the P* colour plane is then dithered and sentto, for example, row 1 of the multi-colour print head cartridge, whilethe data of the L* colour plane is dithered and sent to, for example,row 3, and the data of the O* colour plane is dithered and sent to, forexample, row 5 (steps 19-30).

The above processes achieves the separation of a single colour plane ofthe original source image into a number of fake colour planes so as tofool a multi-coloured print engine and print head cartridge intotreating a monochrome image as a multi-coloured image. In this manner,the monochrome image is printed by several rows of nozzles instead ofone, as shown in step 19-40. However, a problem still exist in the factthat a multi-coloured print engine and print head cartridge is designedto fire each row of nozzles such that the dots ejected by each row ofnozzles land over dots ejected by an upstream row of nozzles. If this isleft unchanged, the monochrome Yellow image represented by the fake‘pink’, fake ‘lime’ and fake ‘orange’ colour plane data will not beproperly reproduced on the print media.

To have the multi-coloured print engine and print head cartridge ejectsdots from different rows onto different lines of the print media, thespeed of print media propagation past the print head cartridge isincreased. The actual increase in print media propagation speed dependson the nozzle firing timing used by the multi-coloured print engine, butessentially causes each row of nozzle to “miss” its dot landing positionby some amount determined, for example, through simulation/calculation.The simulation/calculation ensures that each row of nozzle is ejectingdots to within 0.5 dot pitch of their expected new landing position. Inthe example, of FIG. 19, the print media is propagated past the printhead cartridges at 20 inches per second (IPS) such that the row 1 of oneprint head (PH1) prints every 3^(rd) line starting from line 1, whilstrow 3 of the same print head (PH1) prints every 3^(rd) line startingfrom line 2, and row 5 of the same print head (PH1) prints every 3^(rd)line starting from line 3. Unused rows 2 and 4 may be used to compensatefor dead nozzles in any of rows 1, 3, and 5 or to increase printdensity.

Step 19-40 shows the final image printed by one print head, which is aninterleaving of pink, lime, and orange lines. However, in recognitionthat the pink, lime, and orange lines are fake colours and are in factall lines of the original Yellow colour plane of the original sourceimage, the final image is actually the whole Yellow monochrome image ofthe original source image. The printing of the Yellow monochrome imagein this manner has however been executed around 3 times faster comparedto the case where the above processes are not performed. Compared to thecase where the above processes are not performed, 3 rows of nozzlesinstead of 1 have been used to print the Yellow monochrome image.Moreover, the speed of print media propagation has been increased.

The above process is performed for each of the original Cyan, Magenta,Yellow, and Black colour planes (and spot colour plane, if any), and therespective fake colour images generated for each original colour planesent to an individual print head controller module 1-25 a-e andcorresponding print head cartridges 1-20 a-e. In this manner, anexisting multi-coloured print engine and print head cartridge may be usein the system 1-1000 without any substantial modifications to thehardware, apart from increasing a speed of print media propagation.

The same steps of further processing data to compensate formisalignments of print head cartridges and print head tiles, asdescribed above with reference to FIGS. 17A and 17B, whilst notspecifically described above with reference to FIGS. 18A, 18B, and 19are also performed in like manner to account for vertical and horizontalmisalignments, as well as paper wobbling.

Although the invention has been described herein with reference to anumber of specific embodiments, it will be appreciated by those skilledin the art that the invention is not limited only to the disclosedembodiments, and that these embodiments described a best-mode/preferredembodiment, whereas the invention may be embodied in other formsencompassed within the scope of this invention.

1. A printing method, comprising the steps of: receiving a colour imageand separating the colour image into a plurality of distinct colourplanes; dithering a first distinct colour plane to obtain dot data forthe first distinct colour plane; dithering a second distinct colourplane to obtain dot data for the second distinct colour plane; providingthe dot data for the first distinct colour plane to a first print headcartridge for printing by a plurality of nozzle rows of the first printhead cartridge; and providing the dot data for the second distinctcolour plane to a second print head cartridge positioned downstream fromthe first print head cartridge in a direction of print mediapropagation, the dot data for the second distinct colour plane forprinting by a plurality of nozzle rows of the second print headcartridge.
 2. A printing method according to claim 1, further comprisinga step of adding a delay to the dot data for the second distinct colourplane, the delay compensating for the spatial separation of the secondprint head cartridge from the first print head cartridge.
 3. A printingmethod according to claim 1, further comprising a step of verticallyshifting the dot data for the first distinct colour plane by one or morenozzle rows in a direction of print media propagation, to advance anddelay printing of the first distinct colour plane by the first printhead cartridge by one or more nozzle rows, wherein a physicalmisalignment of the first print head cartridge in a direction of printmedia propagation with respect to the second print head cartridge iscompensated.
 4. A printing method according to claim 1, furthercomprising a step of vertically shifting the dot data for the seconddistinct colour plane by one or more nozzle rows in a direction of printmedia propagation, to advance and delay printing of the second distinctcolour plane by the second print head cartridge by one or more nozzlerows, wherein a physical misalignment of the second print head cartridgein a direction of print media propagation with respect to the firstprint head cartridge is compensated.
 5. A printing method according toclaim 1, further comprising a step of reordering the dot data for thefirst distinct colour plane to account for the physical separation of afirst of the plurality of nozzle rows of the first print head cartridgefrom a last of the plurality of nozzle rows of the first print headcartridge.
 6. A printing method according to claim 1, further comprisinga step of reordering the dot data for the second distinct colour planeto account for the physical separation of a first of the plurality ofnozzle rows of the second print head cartridge from a last of theplurality of nozzle rows of the second print head cartridge.
 7. Aprinting method according to claim 1, further comprising a step ofhorizontally shifting the dot data for the first distinct colour planeby one or more dot pitches in a direction normal to a propagation ofprint media, wherein a wobbling of the print media in a direction normalto the propagation of print media is compensated.
 8. A printing methodaccording to claim 1, further comprising a step of horizontally shiftingthe dot data for the second distinct colour plane by one or more dotpitches in a direction normal to a propagation of print media, wherein awobbling of the print media in a direction normal to the propagation ofprint media is compensated.
 9. (canceled)
 10. (canceled)
 11. (canceled)